Before defining what a dangling participle is, it is good to define the term participle. A participle is simply an adjective that comes from a verb. For instance a working husband. Therefore, working here is a participle used to describe the husband status.
A dangling participle is an adjective that is inadvertently modifying the wrong noun. For example, “Walking across the field, a thorn pricked me.” From this sentence, it seems like it was the thorn walking, which is not correct. Walking is the participle but unconnected to the person who was pricked by the thorn hence a dangling participle.