According to Mattoso Câmara “the name of agreement is given in grammar to the circumstance that an adjective varies in gender and number according to the noun to which it refers (nominal agreement) and that a verb varies in number and person according to its subject (agreement verbal). There are, however, special cases that lend themselves to doubt”.
So, we observe and we can define it as follows: agreement comes from the verb to agree, that is, it is an agreement established between terms.
the case of verbal agreement it concerns the verb in relation to the subject, the first must agree in number (singular or plural) and person (1st, 2nd, 3rd) with the second.
already the nominal agreement it concerns the noun and its referring terms: adjective, numeral, pronoun, article. This agreement is made in gender (male or female) and person.
As we saw above, in Mattoso Câmara's definition, there are general rules and some special cases that should be studied in particular, as they raise doubts as to their use. There are many cases where the standard is not defined and there are different resolutions by authors, writers or students of agreement.
See this subject in more detail in the following links: Verbal Agreement – General Rule and Verbal Agreement – Special cases.
By Sabrina Vilarinho
Graduated in Letters
Source: Brazil School - https://brasilescola.uol.com.br/gramatica/concordancia-verbal-nominal.htm