Mood refers to the happiness of the maid. It can be increased or decreased with certain dialog options, as well as decrease with offline time.
The amount of mood that is decreased with offline time, and the amount of that time, is defined in constants in decreaseMaidMoodValue and decreaseMaidMoodMinutes.
An example of dialog options that increase/decrease mood is Rebecca (11000758)'s script IDs 30-32.
Upon beginning dialog with Rebecca, if the option "Let's chat!" is available, the dialog will be redirect to script IDs 30-32.
The scripts then present multiple dialog branches, all of which can decrease or increase mood, as seen in the server-sided npcScriptFunction.
Depending on the mood meter, the maid mood varies from normal (So-So), good (Good) and very_good (Very Good).
The mood then in turn affects the craft time of any recipe the maid manufactures, as seen in either MaidRecipe tables, as well as the jackpot rate, as seen in MaidGradeInfo.
Mood can also affect dialog conditions, as seen by the attribute maid_mood_time.
Though it is unclear what exactly maid_mood_time means, it may refer to the amount of seconds since mood was last modified. So in the example of most maids, the player would be able to go through the mood-raising dialogs only 30 minutes after they last through went them.