Momentum
Also called Linear momentum
Momentum is the product of an object's mass and its velocity, p = mv. It is a vector pointing the same way as the velocity and is measured in kilogram meters per second, so in one dimension its sign records which way the object is moving.
Every moving object carries momentum, and only two things set how much: how much mass is moving, and how fast.
That is the form printed on the AP Physics 1 equation sheet, and EK 4.1.A.1 defines linear momentum by it. Units are kilogram meters per second, , which has no shorter name.
It is a vector. EK 4.1.A.2 states that momentum has the same direction as the velocity. In one dimension you carry that in a sign: declare a positive direction before writing anything, and a 0.5 kg ball moving left at 3 m/s has momentum of kg m/s, not .
It is not kinetic energy. A 1000 kg car at 10 m/s and a 10 kg cart at 1000 m/s both carry 10,000 kg m/s of momentum, but the cart has 100 times the kinetic energy. Momentum is linear in speed; kinetic energy goes as the square. That single difference is why the two quantities answer different questions about a collision.
Momentum earns its place because of what it does in interactions: the total momentum of an isolated system does not change, whatever happens inside. Using that fact to find a final velocity is a procedure, and it lives in conservation of momentum. What is conserved in a collision separates it from the energy question.