Chicken runs are a screened in area that is usually attached to the chicken coop as part of the structure, an attachment to the structure or both like in the picture above.
This is the area your birds will use to stretch their legs, get a little exercise, forage for bugs, eat some grass, and socialize with other members of the flock. As you can tell this is a pretty important part of your flocks home.
Unfortunately most all of the coops sold are sold based on the number of birds that can be housed in the coop itself not on the available space in the run.
Many, but not all of the coops that are sold come with a small run attached (some are just the coop without any enclosure).
Having a run is a good thing since it's important to have a protected area where they can enter and leave the coop and at least move around a little bit and do some of the things they like to do.
The problem is that in many coops it is such a small space that there really isn't sufficient room for your flock to get any exercise or really move around.
Additionally too small of a space leads to overcrowding which leads to stress, tension, and even bullying which isn't good for your hens or for your egg production.
Also they will basically strip it bare of any vegetation pretty quickly and they will fill it with manure fairly quickly which means more cleaning more often.
Keeping the run and the coop clean and maintained is important for the health of your flock so you really don't want to neglect removing the manure from the coop and run on a consistent basis (in a very small space this could mean daily).
Putting down some straw or other type of bedding will help with this and it's ok to leave some of the area as dirt since chickens enjoy a good dust bath every now and again.
Most coops with built in chicken runs don't have enough space to meet the chickens needs. Ideally you will want a minimum of 9-10 square feet per bird. that means that if you have 4 birds, you'd like to have approximately 40 square feet of run space (for example a 5' x 8' space), of course more is better and allowing them to free range during the day would be ideal.
Allowing your chickens to free range may not be practical unless you have a huge lot and most of us raising backyard chickens don't. In that situation, adding an additional run to your coop is the next best thing.
An additional run will allow them to live a more normal, healthy, and contented life.
For this reason we recommend building or purchasing a chicken run to attach to your coop that will allow you to get as close as possible to the ideal space per bird.
If you can't allocate that exact amount of space, that's ok. Just adding some additional space is still a good thing.
Chickens are like any other animal or pet. If they are enclosed in too small of a space it will affect them physically and emotionally and it's just not healthy.
Having a nice sized run for your flock will help to keep them happy and healthy!