Minor pentatonic is a very common scale that is used for both creating bass lines, and improvising solos. Penta means 5, so there are only 5 different notes in this scale before you are back to a root.
Here is the most common form of an A minor pentatonic scale in the 5th position. The numbers indicate the fingering, and the numbers in parentheses indicate the root of the scale. The root is the primary note that the scale is built from. In the case of an A minor pentatonic scale, the root is an A note. This scale is moveable, so if you were to move every note up 2 frets, this same scale shape would be a B minor pentatonic scale. To get other minor pentatonic scales you just need to line the numbers in parentheses up with the root you are looking for. Of course you need to have a good knowledge of where the names of the notes are on the neck of the bass guitar to quickly move the scale form around to suit your needs.