The phrase "options button" refers to a clickable element on a device or software that offers various choices or settings to customize or control a specific function or feature. Full definition
Press options button next to each spell to find out more about them. (gearnuke.com)
The ability to switch between two of the characters by using the Start / Options button while playing the enjoying the games story missions while in single player. (blastawaythegamereview.com)
When there is an email option button, I can do that easily. (wellnessmama.com)