The next term in the following series is ABB, BCF, CDL, ?

A compound letter term that bundles three letters together is really three independent sub-series running side by side, one per letter position. Solve each position's own rule on its own -- either a simple one-step alphabetical shift, or a numeric pattern read off each letter's alphabet-position number (A = 1 ... Z = 26) -- then recombine the three solved positions to read off the next term.

1. Write each given term as three separate letter positions: Term 1 = (A, B, B), Term 2 = (B, C, F), Term 3 = (C, D, L).

2. First position: A, B, C -- each term's first letter is exactly one step ahead of the previous term's first letter, so the fourth term's first letter is D.

3. Second position: B, C, D -- the same one-step-ahead rule applies, so the fourth term's second letter is E.

4. Third position, converted to its alphabet-position number (A = 1 ... Z = 26): B = 2, F = 6, L = 12. The jump from B to F is +4, and the jump from F to L is +6 -- each jump is exactly 2 more than the jump before it. Continuing that rule, the next jump is +8, giving 12 + 8 = 20.

5. Convert 20 back to a letter: the 20th letter of the alphabet is T.

6. Recombine the three solved positions: D, E, T -> DET.

An independent check on the third position: 2, 6, 12, 20 are exactly n(n+1) for n = 1, 2, 3, 4 (1x2, 2x3, 3x4, 4x5) -- a standard product-of-consecutive-integers pattern -- which confirms 20 (T) as the fourth value without relying on the jump-by-jump count.

So the next term is DET.