A saprophyte or saprotroph is an organism which gets its energy from dead organic matter. This may be decaying pieces of plants or animals. This means that saprophytes are heterotrophs. They are consumers in the food chain.
This is the typical life-style of fungi. Some fungi are parasites on living organisms, but most are saprophytes. Many bacteria and protozoa are also saprophytes. To put it simply, most dead organic matter is eventually broken down and used by bacteria and fungi. Lastly, slime moulds are also saprophytes, as well as consuming bacteria.
Other terms, such as 'saprotroph' or 'saprobe' may be used instead of saprophyte. Strictly speaking, -phyte means 'plant'. The problem is that no embryophytes (land plants) are true saprotrophs, and bacteria and fungi are no longer considered plants. Nevertheless, saprophyte is such a well-known term that most writers continue to use it.