Interactions in Sunless Sea are text dialogues that require you, the player, to decide which action to take.
On this wiki, Interactions are usually described as being the main dialogue category where other choices - actions - can be taken.
For instance, when you first dock in London, you can either go to Your Lodgings or London. These two places will open different choices that you can take, hence they are interactions and the choices are actions.
Whenever an action is mentioned on this wiki, it will be represented by a teal colour.