This character is a Other Symbol and is commonly used, that is, in no specific script. The character is also known as strong and muscled.
The glyph is not a composition. Its East Asian Width is wide. In bidirectional text it acts as Other Neutral. When changing direction it is not mirrored. U+1F4AA prohibits a line break after it, if it’s followed by an emoji modifier.
The CLDR project calls this character “flexed biceps” for use in screen reading software. It assigns these additional labels, e.g. for search in emoji pickers: biceps, comic, flex, muscle.
This character is designated as an emoji. It will be rendered as colorful emoji on conforming platforms. To reduce it to a monochrome character, you can combine it with Variation Selector-15: 💪︎ The character can be changed in appearance, if it is followed by an emoji modifier. See the Emojipedia for more details on this character’s emoji properties.
The Wikipedia has the following information about this codepoint:
The biceps or biceps brachii (Latin: musculus biceps brachii, "two-headed muscle of the arm") are a large muscle that lies on the front of the upper arm between the shoulder and the elbow. Both heads of the muscle arise on the scapula and join to form a single muscle belly which is attached to the upper forearm. While the biceps crosses both the shoulder and elbow joints, its main function is at the elbow where it flexes the forearm and supinates the forearm. Both these movements are used when opening a bottle with a corkscrew: first biceps screws in the cork (supination), then it pulls the cork out (flexion).