It means to use it in a way that is very general and is often used in an ironic way. "They were using the term loosely when the called this a 'conference.' Its a disorganized mess." "They served us.... (and I am using the term losely) ... a "lunch" midway through, but it was literally a banana and a soda." "They had a bunch of so called experts giving presentations on random topics, but the presentations were amateur. They really used the term expert losely."

So, to use a term "loosely" simply means that you are deviating from its strict meaning and applying it in a much more interpretive manner.

In this case "loosely" means "imprecisely". "The gentleman in question, using the term 'gentleman' loosely, was in an inebriated condition." In this example, the speaker is referring to a man who, the speaker considers, does not really count as a gentleman, perhaps because of his discourteous behaviour.