The incumbent is the current holder of a political office. This term is usually used in reference to elections, in which races can often be defined as being between an incumbent and non-incumbent(s). For example, in the 2012 United States presidential election, Barack Obama was the incumbent, because he had been the president in the previous term while the election sought to determine the president for the current term. A race without an incumbent is referred to as an open seat. 

The word "incumbent" is derived from the Latin verb "incumbere", literally meaning "to lean or lay upon" with the present participle stem "incumbent-", "leaning a variant of "encumber," while encumber is derived from the root "cumber", most appropriately defined: "To occupy obstructively or inconveniently; to block fill up with what hinders freedom of motion or action; to burden, load." 

In general, incumbents have structural advantages over challengers during elections. The timing of elections may be determined by the incumbent instead of a set schedule. For most political offices, the incumbent often has more name recognition due to their previous work in the office. Incumbents also have easier access to campaign finance, as well as government resources (such as the franking privilege) that can be indirectly used to boost a campaign. An election (especially for a legislature) in which no incumbent is running is often called an "open seat"; because of the lack of incumbency advantage, these are often amongst the most hotly contested races in any election.
Do challengers have a higher chance of being recognized?
the incumbent often has more name recognition due to their previous work in the office