What's the definition of streak
In terms of Snapchat streaks... This is a number of days two users have been sending a picture or video to each other. In the general term of a streak... An irregular line left from smearing or a continuous series of like events. It all depends on the context.
Generally, the old fashioned term I'm familiar with is to "Walk or run while naked " This is usually thought of as being naked in public, but it can also be what you do after a long day of work when you get home.