It’s a padlock. The bottom is square with rounded edges. Inside the square is four filled in circles in a line from the left to the right. On top of the square is an eclipse shape symbolizing the hooped part of the lock.
This is a Password icon. We've made it in iOS style
, first introduced in iOS version 7 and supported in all later releases up until now (at least iOS 11). This style is based on thin two-pixel lines and is optimized for 50x50 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 13,300 icons, all in the same style and quality.