IVF stands for In Vitro Fertilisation. In vitro is the opposite of in vivo (in the body) and means outside the body. ICSI stands for IntraCytoplasmic Sperm Injection, which means injecting a single sperm into the cytoplasm of a single egg. The cytoplasm refers to the inside of any cell other than the nucleus. ICSI is only done as part of an IVF cycle.