Search Engine Optimization (the tactics and techniques used to get your website ranked so it appears early when someone searches for your product, business or service) has long been a generalized term used for everything related to performing online.
By long, of course, we mean "since the internet and websites and search engines, like Google, were a thing."
In recent years, with the advent of social media, and rampant digital marketing, the game has changed. Aside from the necessary steps of having good copy and relevant content, most SEO strategy has moved off of the website itself.
Now we have SEM. Search Engine Management involves the strategy to optimize the entire web presence & dash; what does the entire internet think of your business across all platforms? Not, what does one search engine think of my website. 
It's actually a lot like a high school cafeteria. SEO assumes that there is only one "cool kids" table (this would be an optimized website) and that any kid at school will find that table, and want to sit there.
SEM knows that there are lots of tables and that the only way to find the one that's the right fit, the cool kids' table, is to look around the whole cafeteria. What table both looks cool, and is the one everyone from jocks to geeks talks about?
The lunch line? That's like Twitter. If everyone in line is talking about a table, then that's a table to pay attention to. Facebook? Remember those groups of kids who hover, talking, drawing attention to themselves before deciding where to sit– which is the same place they always sit.
Pinterest? Think year book photos of a bunch of kids yucking it up at lunch time, at the cool kids' table.
E-mail campaigns are, essentially, notes sent home from school and their all about the cool kids' table.
So, if the internet is nothing but a big, noisy, high school cafeteria, where does that leave SEO and SEM?
First, remember that the terms are not interchangeable and a strategy that does not include both will not be effective. No one will find, much less want to sit at your table, unless you've got good SEO and a SEM strategy.
But, SEM is relatively new thinking. There are no experts at SEM. As we move into an era when search engines update their algorithms more frequently than most businesses update their website, most SEO companies have been left behind. The fact is that the business must be involved in creating and implementing a complete digital marketing strategy. This is true SEM. Think SEM sounds like a bit too much to manage? No worries, firms like Business Actualization know how to look at your current website, apply great SEO strategies and work with you to organize your SEM.
It could be worse; it could be lunch at a high school cafeteria. Now THAT is something none of us wants to try to manage, ever, again.
