The Śiva·sūtras, technically akṣara·samāmnāya, variously called māheśvarāṇi sūtrāṇi, pratyāhāra·sūtrāṇi, varṇa·samāmnāya, etc., refer to a set of fourteen aphorisms devised as an arrangement of the sounds of Sanskrit for the purposes of grammatical exposition as carried out by the grammarian Pāṇini in the Aṣṭādhyāyī.
[1][2] Pāṇini himself uses the term akṣara·samāmnāya whereas the colloquial term "Shiva sutra" is a later development, as per claims by Nandikeśvara in his Kāśikā, that the god Śiva sounded his drum fourteen times to reveal these sounds to Pāṇini.
[1][2][3] Each verse consists of a group of basic Sanskrit phonemes (i.e. open syllables consisting either of initial vowels or consonants followed by the basic vowel "a") followed by a single 'dummy letter', or anubandha, conventionally rendered in upper case and named 'IT' by Pāṇini.
2. r̥ l̥ k, 3. ē ō ṅ, 4. ai au c, 5. ha ya va ra ṭ, 6. la ṇ, 7. ña ma ṅa ṇa na m, 8. jha bha ñ 9. gha ḍha dha ṣ 10. ja ba ga ḍa da ś 11. kha pha cha ṭha tha ca ṭa ta v 12. ka pa y 13. śa ṣa sa r 14. ha l 2.
~na ma ~Na Na na m, 8. jha bha ~n 9. gha Dha dha Sh 10. ja ba ga Da da sh 11. kha pha Cha Tha tha cha Ta ta v 12. ka pa y 13. sha Sha sa r 14. ha l २.
The Akṣarasamāmnāya puts phonemes with a similar manner of articulation together (so sibilants in 13 śa ṣa sa R, nasals in 7 ñ m ṅ ṇ n M).
Economy [α] is a major principle of their organization, and it is debated whether Pāṇini deliberately encoded phonological patterns in them (as they were treated in traditional phonetic texts called Prātiśakyas) or simply grouped together phonemes which he needed to refer to in the Aṣṭādhyāyī and which only secondarily reflect phonological patterns.