This is the 16720th most frequent Turkish word.
yürümesi
The act of walking.
In this sentence, "yürümesi" is used as a noun formed by adding the possessive suffix to "yürüme", meaning "his walking".
Yürümesi bizi şaşırttı.
His walking surprised us.
Here, "yürümesi" is again a gerund that forms the subject of the sentence, describing the act of walking performed by the person (
Onun bu kadar hızlı yürümesi çok ilginçti.
It was very interesting that he walked this fast.
In this example, "yürümesi" refers to the activity of "walking" in a possessive form, framed as a relative activity.