A triad is formed when you take the first, third, and fifth notes of a scale.
It's that simple and yet so many bass lines are constructed from them.
Dance The Night Away is a great example. It's just E and B triads all the way - give it a go!
For more on triads:
Bass Guitar Triad Masterclass
Easy Bass Guitar Triad Exercise
Here's a simple exercise for you that harmonises the C Major scale into seven different triads.
Notice that you get three majors, three minors (m), and one diminished (dim). Make sure to learn the order they appear. You can then move this to different keys.
Make up some bass lines like I do in the video lesson above!
Once you've got that exercise down and memorised the triads formed from a major scale, learn the same thing but with (very useful) seventh arpeggios:
Then, to enter beast mode and reach the summit of bass playing (ok slight exaggeration, but this is gold dust...), learn the arpeggio and mode. Don't worry, it's not that hard but you'll get an incredible amount of mileage from this:
Finally, make up your own bass lines using triads and then listen out for them in your favourite bass lines. This is all part of your ear training and will help with improvising, jamming, writing bass lines, and figuring them out by ear.