The term "Challenge Mode" refers to a difficulty level or gameplay style in which players are presented with specific challenges, obstacles or limitations that make it more difficult to complete a task. This can include limited resources, time constraints, increased enemy difficulty, or other factors that make the game more of a challenge for the player. Challenge mode is often used as a way to provide an additional level of difficulty and replayability for experienced players who are looking for a greater challenge than the standard game provides.