What does this syntax mean?

I see this in a demo file I've been reviewing, which is setting the value of a variable. Is this an if/then/else statement?

b1 >= 0 ? (b1 - b1%50) : (b1 - b1%50) -50

Correct, it's a conditional expression.

If?then:else

Thanks. Appropriately, the sample code is yours 😉