When you test your internet speed, you will be able to notice either one of two things: either your download and upload speeds are close to identical, or your uploads are only a fraction as fast as your downloads. This is because internet connections can be categorized as either symmetrical or asymmetrical.
As you might imagine, symmetrical internet connections are ones which have the same download and upload speed, and which allow these speeds to be used at the same time. Therefore, if you have a symmetrical internet connection, you will be able to upload data (such as videos or music) to the internet whilst you are also downloading large files.
On the other hand, many internet connections are asymmetrical, and these connections tend to favor the download speeds. Often in the case of an asymmetrical connection, download speeds will be much faster, for example it is not uncommon to see a download speed of 10Mbps or more paired with an upload speed of 2Mbps. Aside from limitations previously imposed by older internet connection technology, upload speeds also tend to be lower because most people do far more downloading than uploading. Every website you click on or YouTube video you watch falls under the term downloading, even if you are not actually saving files to your computer, so as you can imagine, this service is often far more important for must users.
Symmetrical connections are becoming more popular amongst competitive service providers such as many super-fast fiber providers who may offer as much as 1GB upload and download speeds to subscribers.