Essentially, both the terms mean to acquire something against money. However, buying is considered a general term, which is most commonly used to refer to everyday goods and commodities. However, purchase is considered to be more of a formal term than buy. RF vs Microwave. RF or Radio Frequency is a term that is often used to describe the number of times per second or oscillation of an electromagnet radiation. Difference Between IUGR vs. SGA. IUGR is Intrauterine Growth Retardation or restriction in which fetal growth is restricted. SGA is a Small for Gestational Age fetus or infant; smaller than 10% of all individuals at that gestational time period. The key difference between thallus and prothallus is that thallus is an undifferentiated filamentous gametophyte of algae, fungi, lichens, and some liverworts while prothallus is the heart-shaped gametophyte of pteridophytes such as club mosses, horsetails, and ferns. Tangerine vs Mandarin. No, this is not about Chinese language that goes by the same name of mandarin, but rather about citrus fruits that has many varieties and subgroups within themselves and appear as oranges to the outside world.