Maintenance is a fee you have to pay in order to make use of any structure. Player ships, such as the Sorosuub Luxury Yacht, while offering a space to store items, are not considered a structure and do not require maintenance or lot spaces.
Houses have different maintenance costs depending on the size. Paying maintenance is usually done in advance through the Structure Management Terminal usually found near the entrance of the building and is the only item within a house that is non-movable. When a house has zero credits in its maintenance pool, it automatically starts deducting from the players bank account.
Houses can also be repacked and stored in your datapad through the Structure Management Terminal, but will still require maintenance.
Other structures, such as harvesters and factories, also require maintenance, however here all must be paid in advance, and they do not automatically deduct from the players bank account as houses do. If the maintenance credit pool is empty the harvester or factory will not work.