A beneficiary is a foreign national for whom an immigration petition is filed and who stands to directly benefit from the petition, such as a visa or green card.
A petitioner is the individual or entity who initiates the immigration petition on the beneficiary's behalf. So, for example, in the context of family-based immigration, the petitioner might be a U.S. citizen or permanent resident related to the beneficiary, and in the context of employment-based immigration, the petitioner may be a US-based company petitioning an H-1B visa on behalf of a prospective foreign employee.
While beneficiaries are generally individuals for whom others have petitioned on their behalf, some individuals, such as certain family members of US citizens and those petitioning for certain employment-based visas, and treaty investor/trader visas, can “self-petition” (i.e., submit a petition on their own behalf), which, in a sense, makes them both the petitioner and beneficiary
Beneficiaries can be classified into distinct categories based on their relationship to the petitioner and the nature of the petition. While there are many categories, the main ones include:
Beneficiaries may be either primary or derivative. Primary beneficiaries are the main individuals on whose behalf a petition is filed. For instance, in an employment-based visa petition, the foreign worker being sponsored is the primary beneficiary.
Derivative beneficiaries, on the other hand, are individuals who derive their immigration status based on their relationship to the primary beneficiary. Commonly, they are spouses or children under 21. For example, if a primary beneficiary is approved for a visa, their spouse and children might also be eligible for visas as derivative beneficiaries.