Apps
steam_osxSteam
● Safe to close
Valve’s game store and launcher.
What it is
Steam’s app and the web helpers that draw its store and library.
If you close it
Any download pauses and games you’re playing through Steam may quit.
The verdict
● Safe to close. An app you can quit with ⌘Q. Save your work first if it asks.
In Activity Monitor
steam_osxsteamwebhelper
From Procession’s guide, in the words the app shows.