Clinical just means that you have been diagnosed with Depression by someone with a bunch of letters after their name, as opposed to colloquial depression, which

Clinical just means that you have been diagnosed with Depression by someone with a bunch of letters after their name, as opposed to colloquial depression, which means something like 'feeling blue'. To be diagnosed you need to meet a number of criteria like 'loss of interest, fatigue' nearly every day for a long period. As far as I know there is no expert consensus on whether depression and Depression are different shades of the same thing or qualitatively different. 'Depression is a chemical imbalance', as a model, is about on par with 'the internet is a series of tubes'. It's not flat out wrong, but it's so oversimplified as to be pretty useless for fixing or making predictions about the system.