I'm going to guess, because I had no idea how to interpret that 'roll' thing either, but there IS a way...
The phrase 'roll with it' seems to get close. So habit, being relaxed about it, but not to the point of numbskulled insensitivity. Got to be some passion, or it isn't even music anymore.
Some people like risk and a bit of flash in a bass player, others want the sound to be like a safe and well-worn road. The best players seem able to do both at the same time, so there's skill, lots of practise, love of what's being done, etc. The biggest way to wreck that comfort of a steady groove is to overreach, to do too much, so some set great store in doing as little as possible while still maintaining that 'roll'.

Personally that would bore me rigid but I can sort of see the point, but a good riff is more effective than working on a single note. Good ostinatos, ground bass, is a very old idea... When a player is comfortable with the mechanics of the instrument, and playing to its strengths, audiences get it, whether they know the instrument or not, they've nearly all heard it when it works, so they do know when it's working, or when it's not.
Last but not least, it's funny, that everyone knows what ROCK is, but not ROLL.

So how exactly has 'rock and roll' been defined, all these years?!