The above answers regarding the technical meaning of momentum are all correct. I would add that momentum is also used outside of the context of science and math where people use it more conversationally. One might say for instance that a project is gaining momentum. This would mean that the project might have started off slow, with only a few people involved, but now it is moving along more quickly and more people have signed on to help. This is also true of political campaigns, kickstarter/crowdfunding/crowdsourcing campaigns anywhere where a critical mass of people is necessary. Momentum when used in this way is often synonymous with gaining traction.

Also, momentum is used in physical science, other sciences, Mathematics, in sports to describe force and speed. But isn't use in conversations for the most part. Hope this helps.

The word momentum is also used in Physics which is a measurable quantity. (Llinear) momentum is product of speed (velocity) and mass. A car has lower momentum than the truck although both may be moving at the same speed. Higher momentum means one needs to apply more force to accelerate or decelerate the moving object (i.e., to change its momentum). The rate of change of Momentum equals the applied force, this is another way of expressing Newtons second law (F=ma).

Hi there! As an English speaker, I use the word "momentum" as another way of saying "speed". It is used rarely though. Generally I think I only use it in a car when, as a car begins to pick up speed, I would say "The car is finally picking up momentum". This is the only time I think I would use it.