The word "supplication" means a humble prayer. Also known as petitioning, it is the most common form of prayer wherein a person asks a deity to supply something.
When a prayer of supplication for money is recited, the person offering the prayer asks the selected deity to grant funds for a particular need. The need may be for the person offering the prayer or for someone else.
Other common prayers of supplication include those petitioning for health, happiness, calming the mind, end to an argument and relationship harmony. Regardless what the supplication is for, the key understanding comes in acknowledging that the prayer person is always the lesser person in the relationship with the deity.