The large black wires, at the bottom, bring power to the home from the outside.  These should be a continuous from the meter. In this case they have been joined (spliced) as evident by the blue and black caps and electrical tape.

It is a sign of poor workmanship and the cutting of corners as evident by numerous other deficiencies within the panel.

The latest electrical work to this home was probably done without a permit and other problems likely exist in the branch wiring. Amateurish electrical work increases the chance of fires and electrical shock.