FHA defines a first-time homebuyer (FTHB) as an individual who has had no ownership in a principal residence during the 3-year period ending on the date of purchase (closing date) of the property.
A FTHB includes any individual that has only owned with a former spouse while married.
A FTHB would also include an individual who has only owned a principal residence not permanently affixed to a permanent foundation, or a property that was not in compliance with State, local, or model building codes and cannot be brought into compliance for less than the cost of constructing a permanent structure.
However, some grant programs impose additional income restrictions on the participants for eligibility as a FTHB. You should contact the specific agency provider to determine the definition of FTHB for each specific program.
HUD's definition of a first time homebuyer is found under Title 24 of the Code of Federal Regulations available at: https://www.govinfo.gov/content/pkg/CFR-2011-title24-vol1/pdf/CFR-2011-title24-vol1-sec92-2.pdf