As moisture levels or humidity increases in your home, it can cause wood floors to buckle. Wood will absorb moisture into its cells causing them to expand.
Most of this expansion will occur across the width of the boards, not the length. This expansion will result in wood floors cupping or buckling if there was not enough "expansion" room allowed for side-to-side movement when the floor was installed. Wood floors should be installed with the recommended side to side "Gap" as per installation instructions, to allow for this movement. If your floors are "cupping" or "buckling", it is important to find out why it is happening. Water leaks, high humidity, damp basements or crawl spaces, etc. can damage floors and promote mold growth. Home inspectors may call out a cupped or buckled floor as a trip hazard and will try to note the moisture issues that might be contributing to the situation.