For most people, the word "fashion" means "clothes". But people may ask the question, "What clothes are in fashion?" And they use the adjective "fashionable" in the same way:
"She was wearing a fashionable coat. His shirt was really a fashionable colour."
But of course there are fashions in many things, not only in clothes. There are fashions in holidays, in restaurants, in films and books. There are even fashions in school subjects, jobs…and in languages.
Fashions change as time goes. If you look at pictures of people or things from the past, you will see that fashions have always changed. An English house of 1750 was different from one of 1650. A fashionable man in 1780 looked very different from his grandson in 1860.
Today fashions change very quickly. Some of this is natural. We hear about things much more quickly than in the past. Newspaper, radios, telephones and television send information from one country to another in a few hours. Newfashions mean that people will buy new things, so you see there is money in fashion.