"Antibody or serology tests look for antibodies in your blood that fight the virus that causes COVID-19."
https://www.cdc.gov/coronavirus/2019-ncov/testing/serology-overview.html
"In general, a positive antibody test is presumed to mean a person has been infected with SARS-CoV-2, the virus that causes COVID-19, at some point in the past. It does not mean they are currently infected."
https://www.cdc.gov/coronavirus/2019-ncov/lab/resources/antibody-tests.html
"SARS-CoV-2 antibody (often referred to as serology) tests look for antibodies in a sample to determine if an individual has had a past infection with the virus that causes COVID-19. COVID-19 antibody tests can help identify people who may have been infected with the SARS-CoV-2 virus or have recovered from a COVID-19 infection."
https://www.fda.gov/medical-devices/coronavirus-covid-19-and-medical-devices/antibody-serology-testing-covid-19-information-patients-and-consumers
"COVID-19 antibody testing, also known as serology testing, is a blood test that's done to find out if you've had a past infection with SARS-CoV-2, the virus that causes coronavirus disease 2019 (COVID-19). An antibody test can't determine whether you're currently infected with the COVID-19 virus."
https://www.mayoclinic.org/tests-procedures/covid-19-antibody-testing/about/pac-20489696
"According to Dr. Omid Bakhtar, a board-certified pathologist at SHARP Healthcare, the COVID-19 antibody test was created in the early days of the pandemic as a way for doctors to diagnose if someone previously had the coronavirus. It looked for antibodies to the nucleocapsid protein, which only appears in those who recovered.
When the COVID-19 vaccines were created, Dr. Bakhtar says researchers wanted a way to determine if the antibodies were taking hold within a person’s immune system. Since the vaccines don’t contain SARS-CoV-2, the virus that causes the coronavirus, the nucleocapsid test would not work. Instead, the vaccines contain a spike protein, which is found on the surface of the virus that causes COVID-19. A separate antibody test was created to check for that."
https://www.khou.com/mobile/article/news/verify/coronavirus-verify/yes-it-is-possible-to-tell-the-difference-between-covid-19-antibodies-and-vaccine-antibodies/536-5a89ec83-4cd3-43ea-bba8-45dee1775323
Antibody Testing Is Not Currently Recommended to Assess Immunity After COVID-19 Vaccination: FDA Safety Communication
https://www.fda.gov/medical-devices/safety-communications/antibody-testing-not-currently-recommended-assess-immunity-after-covid-19-vaccination-fda-safety