SEO
SEO (search engine optimization) is the practice of making a site easier for a search engine to find, understand and prefer, so that its pages appear for the queries they genuinely answer.
It divides into three parts that fail independently. Technical SEO is whether a crawler can reach and render the page at all. On-page SEO is whether the content answers a real query well enough to deserve the position. Off-page SEO is whether anyone else on the internet points at it.
The part most often mistaken for the whole is on-page, because it is the part you control alone. The part most often neglected is internal linking, which is technical and on-page at once: a page nothing links to is a page a crawler finds late and weights at nothing, however good it is.
The word "optimization" oversells the control involved. Nobody optimizes a ranking; you make a page more deserving of one and the engine decides.