, a palatal
sound is one in which the tongue
is placed on or near the hard palate
in the centre of the mouth.
This is narrower than Webster 1913's outdated definition below, which includes sounds such as k that are made on the velum or soft palate: these are now called velar sounds, not palatal.
The most common palatal sound in the world's languages is the approximant (or semivowel) that is the y consonant-sound of you, yes, union. The phonetic symbol for this is [j] (as in German ja), though in English-language (especially US) phonetics, [y] is often used. I would estimate that most of the world's languages have this sound.
The palatal nasal occurs in French and Italian, written gn, and in Spanish written ñ, and in many others: it is like the group ny but simultaneous. (I can't show the phonetic symbol for it.)
The palatal lateral occurs in Italian written gl, and in Spanish in those dialects in which ll has a sound like ly.
The voiceless palatal fricative occurs in German ich, Reich (the different sound in ach is velar), in Japanese hito, hyaku, in Greek okhí 'yes', and may sometimes be heard in English huge: somewhere between a strong h and a thin sh. The phonetic symbol is [ç]. This is sometimes known by the German name of ich-Laut.
The voiced equivalent is very rare, but does occur at the beginning of Icelandic Gísli. There is no known language that has this sound distinct from the much commoner [j] sound; in fact until quite recently the IPA had no symbol for it.
Palatal plosives are not all that common. Hungarian has them, written ty and gy, as in the common name György; and Modern Greek has one at the beginning of kefáli 'head'. They sound exactly intermediate between ky and ty (voiceless), or between gy and dy (voiced). They seem to be naturally unstable and often change into other sounds, such as the English postalveolar affricates ch, j. The phonetic symbol for the voiceless one is [c], but because of the relative scarcity of the sound, the symbol is often co-opted for use with different phonetic values (e.g. ch or ts).