The lowest load bearing part of the building that usually goes underground is a footing or foundation. There are three main types – strip footing, raft (mat) footing and isolated (pad) footing used in the construction field. 
There are sub types under these which are used in certain types of soil and construction requirements which are presented in the slides bellow. The images will also help you better understand this and make the clear view at the foundation area. Take a look!
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