When branching on variables, the branch-and-bound procedure can give priority to branching on the binary variables first, or it can make an intelligent guess as to the next best variable to branch on, regardless of whether it is binary or general. The Priority field controls how LINGO makes this branching decision.

If you pull down the drop-down box for Priority, you'll find the following:

Select Binary to have LINGO give branching priority to the binary variables. Select LINGO Decides to have LINGO select the next integer variable for branching based on an intelligent guess, regardless of whether it is binary or general.

The default is LINGO Decides, which should generally give the best results.