It’s very simple.
Every Retirement Plan has a limit. For example, the current 401(k) limit is $18,000 per year (that’s all you can put in there).
Max out means you fill the plan to it’s limit (aka you put the full amount of $18,000 in your 401(k)).
Front load means you fill it as early in the year as you can (for example instead of putting $1,500 in your 401(k) every month, you put $3,000 in there for only 6 months, or $6,000 in there for 3 months).
Did you understand?