Alveolar Consonant
Alveolar consonants are articulated with the tongue against or close to the superior alveolar ridge, which is called that because it contains the alveoli (the sockets) of the superior teeth. Alveolar consonants may be articulated with the tip of the tongue (so-called apical consonants), as in English, or with the flat of the tongue just above the tip (the "blade" of the tongue; called laminal consonants), as in French and Spanish. The laminal alveolar articulation is often mistakenly called dental, because the tip of the tongue can be seen near to or touching the teeth. However, it is the rearmost point of contact that defines the place of articulation; this is where the oral cavity ends, and it is the resonant space of the oral cavity that gives consonants and vowels their characteristic timbre.
The International Phonetic Alphabet (IPA) does not have separate symbols for the alveolar consonants. Rather, the same symbol is used for all coronal places of articulation which aren't palatalized like English palato-alveolar sh, or retroflex. To disambiguate, the bridge (, etc.) may be used for a dental consonant, or the under-bar (, etc.) may be used for the postalveolars. Note that differs from dental in that the former is a sibilant and the latter is not. differs from postalveolar in being unpalatalized.
The bare letters, etc. cannot be assumed to specifically represent alveolars. The language may not make such distinctions, such that two or more coronal places are found allophonically, or the transcription may simply be too broad to distinguish dental from alveolar. If it is necessary to specify a consonant as alveolar, a diacritic from the Extended IPA may be used:, etc.. Nonetheless, the symbols
(The Extended IPA diacritic was devised for speech pathology and is frequently used to mean 'alveolarized', as in the labioalveolar sounds, where the lower lip contacts the alveolar ridge.)
Read more about Alveolar Consonant: Alveolar Consonants in IPA, Lack of Alveolars, Alveolar Switching