Capacitation is the final step in the maturation of mammalian spermatozoa and is required to render them competent to fertilize an oocyte. This step is a biochemical event; the sperm move normally and look mature prior to capacitation. In vivo this final step typically occurs after ejaculation, in the female reproductive tract. In vitro, capacitation can occur in sperm that have either undergone ejaculation or have been extracted from the epididymis. Non-mammalian spermatozoa do not require this capacitation step and are ready to fertilize an oocyte immediately after release from the male.
Historically, the term "capacitation" has evolved in meaning and this should be taken into account when consulting sources.