There’s a common understanding of the meaning of momentum, and that is a measure of the rate of change of speed of an object that is moving. If something has a lot of momentum it may be moving fast or is very heavy and hard to disrupt in its path. In general a momentum indicator will show you the speed at which a price is changing, or the energy behind the move. It doesn’t address the actual price level, but just whether the process of the price change is speeding up or slowing down.
There is a way of trading called momentum investing, and this isn’t based on technical indicators of momentum. It’s purely assuming there is a momentum to a price that is going up or down, and trading accordingly. We saw a lot of that type of trading with the high-tech stocks at the turn-of-the-century, and this led to a bubble in their value. Having said that, trading with the trend is a much used basis for making money, so it is a matter of extent and having very good reasons for believing that a trend will continue.