All of the following tags are used during on-page optimization.
Title Tags:
These are html tags that are built into a clients site. When google crawls a site it wants to know what is the most important information. This is why we use title tags.
Example:
an H1 tag (Heading 1) is used on a page to point out the most important and relevant keywords. H1 is more important than H2 which is more important than H3 etc.
H1 text
H2 text
h3 text
paragraph text
Meta Tags:
Meta tags are snippets of text that describe a page’s content; the meta tags don’t appear on the page itself, but only in the page’s code.
Alt Tags:
Alt tags are used on images. When google crawls a site, it can only read the code. Since its a software program, it cannot see images. This is what alt tags are for. An alt tag is put into an image code to tell google what the image is.
Meta Description:
The meta description is a ~160 character snippet, a tag in HTML, that summarizes a page’s content. Search engines show the meta description in search results mostly when the searched for phrase is contained in the description. Optimizing the meta description is a very important aspect of on-page SEO.