The US effectively has five levels of government buyers: federal, state, county, city, and town. Each level contains thousands of agencies with their own budgets and procurement processes — school districts, sheriff departments, courthouses, libraries, parks, transit systems, community colleges, universities, post offices, and more.
SLED stands for state, local, and education. It covers everything below the federal level, including educational institutions, and it is a large market in its own right. County and local contracts are often less complicated and easier to win than federal ones, and they can be quite profitable.
Two useful dynamics to understand:
Agencies are motivated to spend their allocated budgets each fiscal year, because unspent funds can lead to reduced budgets the following year.
Most work stays local: city work is funded by the city, state agencies by the state, and federal facilities by the federal budget, so businesses registered in an area have a natural advantage for that area's contracts.