Articulations make your bass playing sound amazing. They consist of hammer-ons, pull-offs, ghost notes, slides, string bends, and vibrato. The last two feature in this lesson.
For more on bass guitar articulations study this lesson:
Bass Guitar: Hammer Ons, Pull Offs, Ghost Notes, String Bends, Slides and Vibrato
Here's one of the most beautiful bass solos ever with plenty of soulful vibrato and blues-inspired bends.