What does 'Maximum load' usually mean when associated with a Bank account?

The "load" is the act of you directly putting money into the account for the card. The "maximum load" is thus the most possible money you can add to the account at one time.

What makes this different from a "maximum balance" is that you can add money to your balance separately from a load - specifically, from getting a refund. So technically you could load 15000 onto the account, spend 5000, load 5000 more, and that would be OK. If you get a refund before you spend more out, however, you would exceed the maximum balance and be in violation of your card agreement - even though you didn't violate the maximum load amount.

The load is also mentioned later in that table, in the form of maximum annual load/spend (which are both unlimited on that card), so this helps to clarify that this "maximum load" is actually the maximum amount you can load at any one time.

Some cards actually have maximum daily/monthly loads which are different than their maximum balances or spend sums, which makes the difference in the definitiosn of "load", "spend", and "balance" to be important distinctions.