It simply means: To buy.
To enter into a long position, you simply buy that asset.
As we all know – if you buy some type of asset – that means at some point in the future, you have to get out of the position.
And to get out of a long position – you simply sell.
Another way of saying the same thing
In a long position, you will have a profit if prices increase.
Conversely, in a long position, you will have a loss if prices decrease.
Going long has unlimited potential profit as prices rise – and unlimited potential loss as prices fall.