1,4-Adduct Definition:

The product obtained from 1,4-addition across a conjugated p system.

1,4-Adduct Explained:

When a conjugated π system undergoes an addition reaction, it forms a product where one group or substituent is added to the first carbon (C1), while the other group is added to the fourth carbon (C4)

In the above example, the reagent Br2 is added to the 1,4 carbons.