The phrase "how far" is primarily used to ask about a distance, either the physical distance between places or the extent to which something happens or is true. It is a question about spatial measurement, for example, "How far is the hospital?" asks for a specific distance. Additionally, "how far" can also inquire about the extent of effort or degree to which someone is willing to go for something, such as "How far will you go to convince someone?".

In simple terms, "how far" asks about:

• The distance between two locations or points.
• The extent or degree of an action or effort.

This distinguishes it from similar phrases like "how long," which is used to ask about time or duration rather than distance.

Thus, "how far" means asking about the length or distance in space or asking about the limit or extent of something happening or being done.