An HTML element is the basic building block of HTML. HTML element defines the structure of an HTML file.
To understand HTML element, let us take the example to print Hello World.
<html> <body> <p>Hello World</p> </body> </html>
In the above example, we have a tag called <p>,
<p>Hello World</p>
That is used to print Hello World.
Now, an HTML element consist of start tag(i.e. <p>), end tag (i.e. </p>) and the content(i.e. Hello World).
In other words <p>Hello World</p> is an HTML element.
Again if we see the <body> tag, the <body> tag along with its content is an HTML element.
<body> <p>Hello World</p> </body>
So, the content for the <body> tag is '<p>Hello World</p>'. And as we have seen in the above example that '<p>Hello World</p>' itself is an element.
So, in simple words, an HTML element can be inside some other tag(<body> tag in this case) and is said to be nested.
Similarly, if we take a look at the <html> tags, the <html> tag, along with its content is also an HTML element,
<html> <body> <p>Hello World</p> </body> </html>