https://www.uscis.gov/news/public-charge-fact-sheet defines public charge:
Background
Applicability and Exemptions
The final rule applies to two types of applicants:
Applicants for admission or adjustment of status to that of a lawful permanent resident (such applicants are subject to the rule’s public charge ground of inadmissibility unless Congress has exempted them from this ground)
Applicants for extension of nonimmigrant stay or change of nonimmigrant status (such applicants are subject to the rule’s public benefit condition unless the nonimmigrant classification is exempted by law or regulation from the public charge ground of inadmissibility)
Definition of Public Charge
The final rule defines public charge as an alien who receives one or more public benefits (as defined in the final rule) for more than 12 months, in total, within any 36-month period (such that, for instance, receipt of two benefits in one month counts as two months).
Benefits Considered
DHS will only consider public benefits as listed in the rule, including:
Supplemental Security Income;
Temporary Assistance for Needy Families;
Any federal, state, local, or tribal cash benefit programs for income maintenance (often called general assistance in the state context, but which may exist under other names);
Supplemental Nutrition Assistance Program (formerly called food stamps);
Section 8 Housing Assistance under the Housing Choice Voucher Program;
Section 8 Project-Based Rental Assistance (including Moderate Rehabilitation);
Public Housing (under the Housing Act of 1937, 42 U.S.C. 1437 et seq.); and
Federally funded Medicaid (with certain exclusions).
Benefits Not Considered
DHS will not consider:
Emergency medical assistance;
Disaster relief;
National school lunch programs;
The Special Supplemental Nutrition Program for Women, Infants, and Children ;
The Children’s Health Insurance Program;
Subsidies for foster care and adoption;
Government-subsidized student and mortgage loans;
Energy assistance;
Food pantries and homeless shelters; and
Head Start.
For applicants which the rule applies to, is receiving food from Salvation Army's food pantry (once a month during the pandemic period) considered public benefit defined by USCIS?
This is the best that I could find about the relation between Salvation Army and the federal goverment: https://www.huffpost.com/entry/the-salvation-armys-white-flag-surrender-to-secularism_b_5003298 says
The Salvation Army receives millions in federal funding, around $188 million in New York alone, to run its homeless shelters, soup kitchens and after-school programs.