a line or band of a different colour from the background
a sample containing micro-organisms, e.g. bacteria, implanted in a line on a solid culture medium, e.g. agar jelly, for growth
an inherent quality, esp one that is only occasionally manifested
a mean streak
He had a mean streak in him
like a streak
informal without a moment's hesitation
He was off like a streak
on a winning streak
enjoying a series of successes or lucky breaks
streak of lightning
a flash of lightning
[Old English strica]