Straight flush: Five cards of sequential ranks of the same suit.
Aces are usually ranked highest but can form part of low sequences too (acting as a '1' instead) - we'd count both A-2-3-4-5 or 10-J-Q-K-A as straights, but the former is 5-high, and the latter is ace-high. When multiple hands of the highest rank are present, the rank of the individual cards breaks these ties. So, here they are, described and ranked from best to worst below.
To make sense of our poker probability calculator's outputs and inner workings, we need to know the different hands you might find in poker.