pronunciation: SHRU-ti ("U" as "u" in "put").
A microtone, that is to say, an interval less than a semitone.
Music treatises ascribe 22 Shruti between Sa and the next Sa. This is because 22 is the smallest whole number that can account for the three types of intervals that were in use in ancient times: the "small" interval, corresponding to the semitone, the "large" interval, corresponding to the whole tone or two times the semitone and the "medium" interval, which lay in between the two, so that it was one and a half times the semitone. Traditionally, Indian musicologists count intervals descending from the high Sa (a point not grasped by certain later musicologists like Pandit Bhatkhande, for which reason their exposition of Shruti is incorrect), thus: the distance (descending) from Sa to Ni, from Pa to Ma and from Ma to Ga was each a large interval; the distance from Dha to Pa and from Re to Sa was each a medium interval and the distance from Ni to Dha and from Ga to Re was each a small interval. Therefore, if the small interval was assigned the unit of 1 Shruti, the medium interval would be one and a half Shruti, leading to inconvenient fractional calculations. So, ancient musicologists assigned 2 Shruti to the small interval, and so the medium interval became 3 Shruti and the large interval became 4 Shruti. Thus the total number of Shruti from one Sa to the next became 22.
In this context, it is worth noting that the Ni of ancient times corresponds to Komal Ni of the present day and the Ga of ancient times corresponds to the Komal Ga of the present day. The ancient note/pitch system was modified by Amir Khusrau (13th century AC) so as to make Sa and Pa fixed (i.e., without any variant form) and all other notes having two forms each. For more discussion on the question of note names and Shruti in Indian art music, see
It is important to bear in mind that Indian music does not follow equal temparament and that the lengths of Shruti at different places relative to the tonic are different.
The concept of Shruti has great practical application in music in most developed musical cultures of the world. In western keyboard music, unfortunately, its application is restricted to the actual fixed tuning of the keyboard instrument. Discounting this for the time being, stringed and wind instrument players in western music, trained to play along the lines of natural temperament, unconsciously apply a good deal of Shruti considerations while playing. This is particularly apparent when a (say) violinist has to play a violin sonata with a pianist where the composer, by oversight or otherwise, did not take into account that the violinist plays according to natural temperament and the poor pianist is bound to the artificial dictates of equal temperament.
A good example is the note C# in the theme of Corelli's La Folia variations for violon and piano, where the note is sounded together by both instruments early in the theme. The piece being in the key of D minor, the violinist naturally feels this note as the leading note and pitches slightly higher with his finger than he would have done to a C# note had it been written in the key of, say, A major, where the note would be a mediant and do not as close to the subdominant as a leading note would be in relation to the next higher tonic. So, in La Folia, when the violinist follows his natural instincts, his C# is actually higher than that of the pianist, who is innocent of all such subtle considerations and plonks away at the only C# he has in that particular register, resulting in a horrible clash between the pitches of the two instruments.
The lay listener, not realising the acoustical problem involved in this case, and unable to believe that a piano can be out of tune (which in fact it is, under the circumstances!), considers the violinist to have had a lapse of intonation! That is to say, in order to maintain his professional prestige, the poor violinist has to actually play out of tune to sound in tune to the listener: an unhappy compromise but a fact of life when playing with a keyboard instrument!
Happily, In Indian art music, such problems do not arise, because the idea of equal temperament is utterly repugnant to Indian music. However, there are other Shruti-induced problems. Shruti do not dictate inviolate and fixed points of pitch, rather, they indicate a sufficiently close neighbourhood of pitches within which the artiste is permitted to pitch his or her note. The very subtle degrees of variation in precise, scientifically measurable pitch for the same note of a Raga differ from artiste to artiste and also for the same artiste from time to time.
This is why if (as has been rather unwisely and ignorantly done) the pitches used by an artiste in a Raga rendering have been calibrated with an oscilloscope or some similar device, these calibrations will be different almost each time he or she renders the same Raga. This will confuse the unmusical analyser hell-bent on Science alone (to the exclusion of emotional and spiritual expression, which ultimately determine the Shruti the artiste does actually use at the moment he/she is using them), but will be perfectly acceptable by the most knowledgeable and sensitive of listeners.
For this reason, although a keyboard instrument like a harmonium is unsuitable for Indian art music, many vocalists prefer to be accompanied by one (where the Shruti are fixed and so predictable) rather than the traditional Sarengi, where the Sarengi player's sense of Shruti may be different from that of the vocalist and so may actually cause a measure of disturbance rather than enhancement. It is only a highly musically evolved Sarengi player who can sublimate his individual Shruti sense and adopt those of the vocalist being accompanied – such a concert will then bring out the finest in the vocalist. Needless to say, such Sarengi accompanists do not lie thick upon the ground and are, in consequence, in great demand!