When you are "on a roll" that means you are having lots of good luck, or are having a series of successes with something. I think this phrase comes from gambling with dice- when you keep winning at dice you are on a roll. Say if you were taking a test and kept answering every question correctly. You'd be on a roll. Sometimes it's used when you have been doing something for a while, and you want to keep doing it because you have a system down for doing it well. Like, if I was making a bunch of western omelets and you asked if I needed help, I'd tell you "no thanks, I'm on a roll".

You mean "in a row".

it may refers to: 1. A series of objects placed next to each other, usually in a straight line. 2. A succession without a break or gap in time: won the title for three years in a row. 3. A line of adjacent seats, as in a theater, auditorium, or classroom. 4. A continuous line of buildings along a street. cowboy...