The term "challenger" has a few different meanings, but generally it refers to someone or something that presents an obstacle, difficulty or opposition. In a more specific context, it can refer to: 1) A company or product that challenges the dominance of another established brand (e.g., Apple's iPhone was a challenger to Nokia's mobile phone market share). 2) An athlete who competes in a sporting event and tries to win by beating an incumbent champion. 3) A political party or candidate that opposes the current government or ruling party, often running on a platform of change or reform.