A term from Sanskrit phonetics, used in English. In the Devanagari script, it is an oblique stroke under a letter, going off to the right, to indicate that it has no vowel.
Syllables are written with a consonant letter, and the vowel is a smaller sign written around it somewhere. If there is no vowel sign, it is considered to have a, the commonest vowel. The virama cancels this a.
The first A of the name is long (written with a macron in print, virāma), so on the Web it may be seen as viraama or virAma.