Space

A creature's space is the area that it effectively controls in combat, not an expression of its physical dimensions.

A typical Medium creature isn't 5ft wide, for example, but it does control a space that wide. If a Medium hobgoblin stands in a 5ft wide doorway, other creatures can't get through unless the hobgoblin lets them.

A creature's space also reflects the area it needs to fight effectively. For that reason, there's a limit to the number of creatures that can surround another creature in combat. Assuming Medium combatants, eight creatures can fit in a 5ft radius around another one.

Because larger creatures take up more space, fewer of them can surround a creature. If four Large creatures crowd around a Medium or smaller one, there's little room for anyone else. In contrast, as many as twenty Medium creatures can surround a Gargantuan one.

Moving Around Other Creatures

You can move through a nonhostile creature's space. In contrast, you can move through a hostile creature's space only if the creature is at least two sizes larger or smaller than you. Remember that another creature's space is difficult terrain for you.

Whether a creature is a friend or an enemy, you can't willingly end your move in its space.

If you leave a hostile creature's reach during your move, you provoke an opportunity attack.