an approach to understanding the nature of complex things by reducing them to the interactions of their parts, or to simpler or more fundamental things or (b) a philosophical position that a complex system is nothing but the sum of its parts, and that an account of it can be reduced to accounts of individual constituents.
That said, one can come to understand the term better when examples are used in connection with the definition itself.
1. A person may not understand how the inside of an animal works. That said, they may understand how mechanics of a watch work. In reductionism, the inside of an animal is compared to that of the inside of a watch (in regards to how everything is inner-connected, have specific functions, and allow the whole to work).
2. A person may not be able to understand the complexities of a religion, or its ideologies. If looking at this idea through a reductionist's lens, the basic ideas of religions would be defined based upon universally accepted ideas. (For example, what is right (not sinning) and what is wrong (sinful).)
3. In brain research, a reductionist would explain mental disorders through the blocking or abundance of chemicals in the brain. (Meaning, depression is caused by inadequate transmission of neurotransmitters.)