What is feature space and how to map into feature spaces?

knn
machine_learning

#1

While studying the KNN algorithm, I came across the fact that KNN assumes data to be in feature space. This fact was given under the assumptions section.for KNN.
Is there any precaution that must be taken for avoiding errors due to presence in feature space?
How does it affect the accuracy of the algorithm?

Regards,
Shashwat