SDV and Signatures are similar measures to mark a form or visit as having valid data entered, being complete, and/or having been checked by a monitor.

Source Data Verification (SDV) - confirms the conformity of the data presented in case report forms with the source data. It is possible to perform SDV on a field, form or a visit.

Other Data Verification - Castor EDC allows to add a custom verification type in the Settings tab.

Signature - the Signature can be applied to indicate that the information is complete, while a monitor will use SDV as a second line of verification of the completeness and adequateness of the data entered. 

Lock - Locking a participant or a part of the study allows to prevent further data entry. In that sense, it is fundamentally different to SDV and Signatures. It is possible to lock visits and forms, as well as a participant.