Idea of Lock Icon
The image is the basic rounded outline of a padlock. The padlock has a U-shaped part sticking out the top where you would loop it through the thing your are locking. Currently it is in the locked position. In the middle of the main, round, body of the lock is a keyhole where the pins of the key would go in pointing down.
This Lock 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 6,200 icons, all in the same style and quality.