Does the 3SAT problems have to have consistent operators?

Question

What are the rules pertaining to 3SAT as to the actual boolean equation?

The main thing I do not understand is in a given boolean expression within a single clause can you have both AND + OR operators i.e. (x1 & x2 | x3) or do they have to remain consistent i.e. (x1 & x2 & x3) or (x1 | x2 | x3)?

That being said when connecting clauses together do the boolean operators have to be consistent?

i.e. (x1 & x2 & x3) & (x1 & x2 & x3) & (x1 & x2 & x3)

or                                                                             

i.e. (x1 & x2 & x3) | (x1 & x2 & x3) | (x1 & x2 & x3)

or can they be mixed up like

i.e. (x1 & x2 & x3) | (x1 & x2 & x3) & (x1 & x2 & x3)

or                                                                             

i.e. (x1 & x2 & x3) & (x1 & x2 & x3) | (x1 & x2 & x3)

Can a 3SAT problem just be a huge jumble of different logic operators or do they have to remain consistent throughout the equation? Ever example I have seen has consistent operators and I cant seem to find the answer to the question anywhere.

Answer 1

3SAT is a problem of deciding satisfiability of boolean formula in 3CNF form: this means that

1. Each clause has either exactly 3 different literals in each clause or at most 3 literals in each clause, according to different definitions.

2. Only $\lor$ operators can be used inside clauses (not counting varible negations).

3. Only $\land$ operators can be used outside clauses.

[General] SAT problem does not have a limit on number of literals in a clause and Circuit SAT allows any boolean formula.