Below is a list of restricted names that cannot be used to name a custom field because it is already a standard (or app critical) system field or object:

activity_logs

app

app_id

atom

atom_dictionary_id

atom_number

approve_url

batch_process_statuses

changed_values

comments

corporation

created_at

curr_state_name

current_host

current_step_ref_id

current_user

deleted_at

documents

email_address

endorsement

fields

histories

id

inspect

last_activity_date

last_activity_name

last_actor

liquid_mode

name

phase

phase_id

reaction_params

recipient

reject_url

relations

requester

roles

underlying_combo_values

user_mappings

view_request_url