The word Semantic means relating to meaning or logi in language. Semantic HTML is a way of writing HTML in a meaningful manner. For exmaple, in Semantic HTML, instead of using <b> </b> for bold, <strong></strong> is preffered.

Similarly, Elements such as <header>, <nav>, <section>, <article>, <aside>, and <footer> act more or less like <div> elements. And used in while implementing semantic HTML practices

An example of semantic element layout by w3schools