What does lub(T1,... Tn) mean?

Question

The following quote is from

JLS 14.20

The declared type of an exception parameter that denotes its type as a union with alternatives D1 | D2 | ... | Dn is lub(D1, D2, ..., Dn).

What is the lub(D1,...Dn) here?

Answer 1

It stands for "Least Upper Bound" and is formally defined in §4.10.4. Least Upper Bound:

The least upper bound, or "lub", of a set of reference types is a shared supertype that is more specific than any other shared supertype (that is, no other shared supertype is a subtype of the least upper bound).

Answer 2

It stands for least upper bound. See JLS 4.10.4.