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 Password icon is made in Material Design style
developed by Google. This style is based on extremely simplified shapes, thin two-pixel lines, and is optimized for 24x24 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 5,700 icons, all in the same style and quality.