For use in inns. The command 'Offer' will make the innkeeper tell you the cost of storing your carried items for one (real life) day. 'rent' will store the items and make you leave the game. The next time you enter, you'll start out in the inn where you left. The inn will store your items as long as you have the gold to pay the rent. Money will be automatically taken out of moneybags to cover the expense.
For playability reasons, rent costs are not linear in time. The first day of rent costs more than the second, which costs more than the third, and so on. As a consequence, players who can't connect for a few weeks won't have to pay an exhorbitant sum when they return.
Players above level 15 (other than Istari) will not be able to rent in some towns as the folk there are simply too suspicious of them. Evil high level players will have to risk going to the forsaken city of Tharbad, while good players should journey to places such as the fair Rivendell.
You can also use the 'rent' command to rent your mobiles (e.g. horses) at stables. Move to a stable, and type 'rent <pet>' in order to do this. You have to lead or ride the mobile you want to rent.
You can retrieve your mobile from the stables by using the "trade" command to return the ticket and get your mobile back.
If your connection to the game breaks, after a while the game will rent you automatically. Note that most of the time this will result in you paying much greater rent costs. You will also be rented automatically if the game crashes or reboots.