In accounting and bookkeeping, float is the time between the writing of a check and the time that the check clears the bank account on which it is drawn.
For example, Payer Corporation writes a check for $5,000 and mails it to a supplier on Wednesday. However, the check will not clear Payer Corporation's checking account until Monday. Hence, Payer Corporation will have $5,000 of float between Wednesday and Monday.
Mary plays the float when she mails her rent check on Thursday even though she does not have a sufficient balance in her personal checking account. She is counting on her paycheck being electronically deposited on Monday morning prior to her rent check clearing her checking account.