No problem
So "SEO" is "Search Engine Optimization". It is a major form of online marketing and involves trying to game the system of Google's algorithm (Google never explains the exact way its search algorithm functions) by doing various things. This includes choosing the right words to publish, making sure you minimize dead links, use proper coding, foster a sense of trust in your information, et cetera.

Doing the opposite will create a penalty for the site. Sometimes that's passive (you keep using a more complex word instead of plain English, for example) and sometime's Google decides you're doing something that's harmful to the way people use websites like yours (overcomplicating the browsing process, for example).

I've taken SEO courses, had meetings with people whose entire job is SEO, and it's still confusing and sometimes backwards.