Explain this joke

Question

Somebody posted this joke in the comments of a joke and I didn't know this one. As I'am new to programming I didn't even understand it.
Pls help 😨
I guess everyone knows this one, but anyways:
what does an IT person wear for costume party?
...
255.255.255.0

Answer 1

It's the network-mask I think…… ^_^

Answer 2

u should ask this to the person who posted this

Answer 3

#ValentinHacker
Makes sense. Thank you!