What you're going to see below is a part of a lesson that my teacher of grammar gave me; I've always thought that head words and main words are the same but now i'm just confused.

1. Difference between Phrase, Clause and Sentence
1. Phrase:
A phrase is a group of words that work together to do one job but do not contain a subject and
a verb.
Grammarians tend to classify phrases in two different ways:
1. Five types according to their main word: Noun, Verb, Adjective, Adverb and Prepositional
Phrases.
2. Six types according to their headword: Participial, Gerund, Infinitive, Prepositional,
Absolute and Appositive Phrases.

anonymousI've always thought that head words and main words are the same but now i'm just confused.

"Head word," or simply "head," is the technical name used by linguists. https://glossary.sil.org/term/head

"main word" is what non-linguists might use because they are unfamiliar with the vocabulary of linguistics.

anonymous2. Six types according to their headword: Participial, Gerund, Infinitive, Prepositional, Absolute and Appositive Phrases.

Comments:

A gerund is a term for the present participle of a verb which functions as a noun in the context of a clause. It is not a phrase type. e.g. Deep-sea fishing requires strength and patience.

There are noun phrases, like this one. the tall, skinny, elegantly-dressed seventy-year-old English woman in a gorgeous new mink coat

An appositive phrase and an absolute phrase are noun phrases. The term "noun phrase" (Nominal) should be in the list, and

Infinitives and participles are verbs, so syntactic units with them are nonfinite clauses, not phrases. The subject may not be explicit, but it can be determined also.

Your list is a mixture of adjectives and nouns, so stylistically, it is not good English.