The mode is the value that appears most often — the tallest bar, the most popular choice, the peak of the pile. It answers "what is the most common outcome?" rather than "what is the central one?".
The mode has a unique power: it is the only average that works for categorical data. You cannot take the mean or median of eye colours, but you can ask which colour is most frequent — that is the mode. For "favourite ice-cream flavour", the mode is the bestseller.
A data set can also have more than one mode. Two values tied for most frequent make the data bimodal; several make it multimodal — often a clue that two different groups are mixed together.
Each bar counts how often a category appears. Slide the middle bar up and down: the marker always jumps to whichever bar is currently tallest — that category is the mode. Make two bars equal in height and the data becomes bimodal.