# Is there standard terminology/notation for the “prefix” of a word?

Given a word like $abbbaaaba$, we can take (say) the first three letters. We might write $$\mathrm{foo}_3(abbbaaaba) = abb,$$ or something like that. Is there any standard terminology or notation here?

• the term is cohomology – mathworker21 Mar 17 '17 at 6:48
• What about "prefix of length 3"? – dtldarek Mar 17 '17 at 6:52
• Prefix seems quite common. – Mauro ALLEGRANZA Mar 17 '17 at 7:05
• @mathworker21: huh? – bertram Mar 17 '17 at 14:35

prefix (of length $3$) is pretty logical, but I am finding a lot of hits for the second obvious thing that came to mind:
initial segment (of length $3$)