Electrical components like batteries and solar panels can be used independently or combined. If combined, they are connected in series or in parallel.1)
Series connections double the voltage while the current (or capacity in Ah when dealing with batteries) remains unchanged.
Parallel connections double the current while the voltage remains unchanged.
Wide parallel configurations (like 4P) are difficult to charge/discharge evenly without exotic cable configurations.
When discussing multi-battery banks it is common to describe the electrical layout with a particular notation.
p = parallel
s = series