Drop-ins: [prob. By Analogy With {drop-outs}] N. Spurious
Characters Appearing On A Terminal Or Console As A Result Of Line
Noise Or A System Malfunction Of Some Sort.
:drop-ins: [prob. by analogy with {drop-outs}] n. Spurious
characters appearing on a terminal or console as a result of line
noise or a system malfunction of some sort. Esp. used when these
are interspersed with one's own typed input. Compare
{drop-outs}, sense 2.
-- The AI Hackers Dictionary