What is the longest running race distance?

I know that the Boston Marathon is 27 miles

 Whats it mAtter if you don't know the speed? Let's all run slow for a long distance, or run fast for a medium distance, who did better?

Technically it's a marathon which is 26.2 miles but you can participate in an ultra marathon which can be anywhere up to 100 miles.

i think it's called half-maraton

marathon is the official longest distance race , .

The 10,000 meter run is about 6.2 miles. A race of this distance is often referred to as a "10K". Common longer distances include 20K, half-marathon, and marathon. 

The 20K is, as you expect, is 20,000 meters. The full marathon is about 42.2 killometers, or about 26.2 miles. The half marathon is about 21.1 kilometers, or about 13.1 miles.

There are distances longer than the marathon, and are called ultramarathons. There are hundred kilometers, hundred miles, and other distances. Some ultradistance runs are measured by time. The winners are those who go the longest distance. For example, there might be a 24 hour run.

Running organizations may keep records of races at standard distances, but they are not inclined to keep records for odd distances. Whatever distance the longest race humans have run is, there is no prohibition against trying to run one longer. 

If you want to try to run longer, I suggest you consult Guinness Word Records to find what the record is for the longest known distance run without significant breaks.

Comment: World Athletics keeps records for standard distances up to the marathon. Ultrarunning organizations may keep records for selected ultramarathon distances.

Comment: I said "without significant breaks" because in road races, it's typical to offer stations with water and sports drink. Although efforts are made to allow runners to receive the refreshment while running, many runners slow down at aid stations. Some may even pause, confident they can make up for it. Longer races may offer porta-potties on the course. Of course, in a race, as long as a runner stays on the course and follows the other rules, how the runner uses his/her time is up to the runner.

There are ultra marathons that may last days. There are 24 hr ultras and ones that are 100 miles or more. Per Wikepedia "The Self-Transcendence 3100 mile race is the world's longest certified footrace." (link 1). Link 2 below lists some of the toughest ultras, some that are hundreds of kilometers. 

Yes, there are a range of ultramarathons. The single day races are 50k, 100k and 100 mile

The marathon is an extremely common race, formalized at 26.2 miles - that you haven't heard of such a thing, despite having an internet connection, is beyond me.

There are also ultramarathons, races consisting of distances longer than 26.2 miles.  25 km and 50 km are common, though some stretch to 100 miles.

A Marathon  ,,  26.2 miles