brackets [...]: sometimes called "square brackets" to distinguish them from curly brackets (braces), but often called simply "brackets".

brackets [...] [1]: symbols which are used to enclose phonetic material. For example, [k] signifies "the phonetic sound k, whether it is phonemic or not". Contrast slashes [4] /.../. [Spanish: corchetes [1]]

brackets [...] [2]: symbols which are used to enclose phrases, clauses, or other (especially syntactic) units. For example, the sentence "We didn't see the doctor that you recommended," consists of the (independent) clause [We didn't see [the doctor [that you recommended]]], which contains the noun phrase [1] [the doctor [that you recommended]], which in turn contains the (dependent) clause [that you recommended]. [Spanish: corchetes [2]]

brackets [...] [3]: symbols which are used to enclose the indication of a feature or a collection of features. For example, [+anterior] means that the indicated sound has the feature anterior (front). A collection of features can be arranged either in-line, e.g. [+anterior, +high, -round], or vertically, e.g.
[Spanish: corchetes [3]]