Simplify the following text for a Grade 14 native English-speaking person.
Original: In physics and mathematics , a pseudovector ( or axial vector ) is a quantity that transforms like a vector under a proper rotation , but gains an additional sign flip under an improper rotation ( a transformation that can be expressed as an inversion followed by a proper rotation ) .
Simplified: In physics and mathematics , a pseudovector ( or axial vector ) is a quantity that transforms like a vector under a proper rotation , but gains an additional sign flip under an improper rotation such as a reflection .