Content clausewikipedia
In grammar, a content clause is a subordinate clause that provides content implied or commented upon by its main clause.
content clauseindirect questiondeclarative content clausethat''-clausesdirect questionreported question

Dependent clause

subordinate clausedependent clausesubordinate clauses
In grammar, a content clause is a subordinate clause that provides content implied or commented upon by its main clause.
The different types of dependent clauses include content clauses (noun clauses), relative (adjectival) clauses, and adverbial clauses.

Interrogative

interrogativeinterrogative sentenceinterrogative mood
There are two main kinds of content clauses: declarative content clauses (or that-clauses), which correspond to declarative sentences, and interrogative content clauses, which correspond to interrogative sentences. For more information see interrogative mood and English grammar.
Indirect questions (or interrogative content clauses) are subordinate clauses used within sentences to refer to a question (as opposed to direct questions, which are interrogative sentences themselves).

Indirect speech

indirect speechindirect discoursereported speech
Reported questions (as in the last of the examples) are also subject to the tense and other changes that apply generally in indirect speech.
In grammar, indirect speech often makes use of certain syntactic structures such as content clauses ("that" clauses, such as (that) he was coming), and sometimes infinitive phrases.

Question

questionwh-questionanswer
Such clauses correspond to direct questions, which are questions actually asked.
As well as direct questions (such as Where are my keys?), there also exist indirect questions (also called interrogative content clauses), such as where my keys are.

Adjective

adjectiveadjectivesadjectival
Similarly with certain verb-like adjectives:
Some nouns can also take complements such as content clauses (as in "the idea that I would do that"), but these are not commonly considered modifiers.

English grammar

Englishgrammarthere is
For more information see interrogative mood and English grammar.
Note that inversion does not apply in indirect questions: I wonder where he is (not *... where is he).

Question mark

question mark????
The question mark is not used for indirect questions.

Subjunctive mood

subjunctivesubjunctive moodPresent subjunctive
Subjunctives occur most often, although not exclusively, in subordinate clauses, particularly that-clauses.

Interrogative word

interrogative pronouninterrogative wordinterrogative
They may be used in both direct questions (Where is he going?) and in indirect questions (I wonder where he is going).

English clause syntax

frontingconditional
Particular types of dependent clause include relative clauses, content clauses and adverbial clauses.

Who (pronoun)

whowhomwho/whom/whose
The same forms (though not usually the emphatic ones) are used to make indirect questions:

English subjunctive

subjunctivesubjunctive moodpast subjunctive
The main use of the English present subjunctive, called the mandative or jussive subjunctive, occurs in that clauses (declarative content clauses; the word that is sometimes omitted in informal and conversational usage) expressing a circumstance that is desired, demanded, recommended, necessary, ''[https://en.wiktionary.org/wiki/vel_sim.

V2 word order

verb-secondV2verb-second word order
They are declarative content clauses, the direct objects of so-called bridge verbs, which are understood to quote a statement.

Subject–auxiliary inversion

subject–auxiliary inversionsubject-auxiliary inversioninversion
Inversion also does not normally occur in indirect questions, where the question is no longer in the main clause, due to the penthouse principle.

Clause

clauseclausesfinite clause
They can also modify a noun predicate, in which case they are known as content clauses.

Uses of English verb forms

past progressivesimplefuture-in-the-past
This commonly occurs in content clauses (typically that-clauses and indirect questions), when governed by a predicate of saying (thinking, knowing, etc.) which is in the past tense or conditional mood.

Pipil grammar

Indirect questions are introduced by either (a)su 'if, whether' or a wh-expression, depending on the kind of question.

Shall and will

shall'' and ''willshallwill
The above meaning of shall is generally confined to direct questions with a first person subject.

English passive voice

passive voicepassivepassivisation
This is particularly the case with sentences containing content clauses (usually that-clauses).

Afrikaans grammar

three gendered pronouns
Word order in Afrikaans follows broadly the same rules as in Dutch: in main clauses, the finite verb appears in "second position" (V2 word order), while subordinate clauses (e.g. content clauses and relative clauses) have subject–object–verb order, with the verb at (or near) the end of the clause.

Infinitive (Ancient Greek)

The same constructional alternation is available in English (declarative content clause -a that clause- or to-infinitive), as shown below.

Interrogatives in Esperanto

As explained above, any interrogative clause can be used as-is as an indirect question, e.g.

English verbs

-edEnglishEnglish regular verbs
Other complements may include prepositional phrases, non-finite clauses and content clauses, depending on the applicable verb pattern.

English relative clauses

relative clausesrelative pronounsnon-finite relative clause
But these pronouns introduce other clauses as well; what can introduce interrogative content clauses ("I do not know what he did") and both whatever and whoever can introduce adverbials ("Whatever he did, he does not deserve this").