BEM — Block Element Modifier

Blocks, Elements and Modifiers Block Standalone entity that is meaningful on its own.

Examples header, container, menu, checkbox, input

Element A part of a block that has no standalone meaning and is semantically tied to its block.

Examples menu item, list item, checkbox caption, header title

Modifier A flag on a block or element. Use them to change appearance or behavior.

Examples disabled, highlighted, checked, fixed, size big, color yellow