An apical consonant is a phone (speech sound) produced by obstructing the air passage with the tip of the tongue. It contrasts with laminal consonants, which are produced by creating an obstruction with the blade of the tongue, just behind the tip.
It is not a very common distinction and is typically applied only to fricatives and affricates. Thus, many varieties of English have either apical or laminal pairs of [t]/[d]. However, some varieties of Arabic, including Hadhrami Arabic in Yemen, realize [t] as laminal but [d] as apical.
Basque uses the distinction for alveolar fricatives, as does Serbo-Croatian. Mandarin Chinese uses it for postalveolar fricatives (the "alveolo-palatal" and "retroflex" series). Lillooet uses it as a secondary feature in contrasting velarized and non-velarized affricates. A distinction between apical and laminal is common in Australian Aboriginal languages for nasals, plosives and (usually) lateral approximants.
Most dialects in the Bengali-Assamese continuum distinguish between dental-laminal alveolar stops and apical alveolar stops. In Upper Assamese, they have merged and leave only the apical alveolar stops. In Western Bengali apical alveolars are replaced by apical post-alveolars.
In the International Phonetic Alphabet, the diacritic for apical consonants is ?̺ COMBINING INVERTED BRIDGE BELOW (HTML