General question about a function used in common equation

[SFCMatt]

Hello all,
As you’ll see by this question I am very new to the game - only about 1.5pm that in.

So far I have no issue reading schematics, translating them to perf or strip board and have breadboarded about a dozen circuits but when I try to dig into the theory and equations used I keep seeing a function used that I just haven’t seen before.

I have attached a screenshot with a basic gain calculation and have circled the equation in question and underlined my issue - the 2 vertical lines on the bottom - can someone explain how to apply this by hand? Is this short form for something longer?
I’m drawing a blank here and it’s frustrating not being able to be able to do my own calcium by hand lol

Any help is welcome,
Thanks!

 

[benny_profane]

That means the resistors are in parallel. It’s cleaner to write it that way so there aren’t fractions in the denominator. To calculate, use the formula for parallel resistance.

 

[SFCMatt]

Wonderful - thanks so much!