The action of registering for or enrolling in something; the process of creating an account or joining a service.
Compound word from 'sign' (from Latin 'signum' meaning mark or token) + 'up' (indicating completion or upward direction). Emerged in the 20th century from the practice of literally signing one's name on enrollment lists.
The phrase captures the physical act of writing your name on a list or form, which for centuries was how people committed to joining something. Even though most signups are now digital, we still use this term that evokes putting pen to paper and making your mark.
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