Header 5 tags, known as H5 Tags are meant to serve as sub headers to your page’s content.
They are the fifth largest & 5th boldest of all tags. Search Engines do not limit the amount of H5 tags they will honor, and they are considered least highest in priority (after URL, Title Tag & H1, H2, H3 & H4 Tags) for the keywords contained in them.
Search engines will honor the first 80 characters contained in each & traditionally the higher up on the page that a tag occurs the more value will be given to its keywords in terms of importance.
H5 Tags & Search Engine Optimization
H5 Tags are typically used the least frequently of all heading tags, but still are meant to contain keywords of higher importance than the regular body content.
Always be sure that the information within your site’s H5 tags is complementary to the rest of the page’s tags & body content, as to not send conflicting keyword topic signals.
Most websites do not utilize H5 tags, as they are more useful for content that is highly detailed & dense to call out things that are important to know about, but not as important as the keywords contained in the other tags on your page.