发送 (fāsòng) specifically means to send or transmit electronically or through a communication system (emails, texts, signals). It's more focused on transmission than 发 (fā), which can also mean issue, express, or distribute, and distinct from 送 (sòng), which covers physical delivery or seeing someone off. 发出 (fāchū) emphasizes the act of sending out a sound, order, or signal from a source.