within

Inside the limits, boundaries, or scope of something. This can refer to physical space, a period of time, or an abstract concept like a set of rules or expectations.

• The package should arrive within three business days. — This indicates a time limit.
• Keep your pets within the fenced yard. — This refers to a physical boundary.
• The decision falls within the mayor's authority. — This describes the scope of power or responsibility.
• We are working within a tight budget. — This refers to financial constraints.

Inside; internally; in or to the interior. Used when the context of the location is already understood or implied, or when referring to one's own mind or being.

• He chose to remain within for the evening. — This means he stayed indoors.
• There's a strength that comes from within. — This refers to an internal, personal source.
• She heard a strange noise from within. — This implies the noise came from inside a building or structure.