入声是音韵学上一组相互关联的概念的统称。

入声韵是指古代汉语中的一类音节结构。入声字是指音节属于这类结构的字。受音节结构影响，这类字的声调在《切韵》时代都相同，因此都属于入声调类，其入声调值的调型是短而急促。入声调类也可以用来特指某个特定时期、某种特定汉语方言中的一个或几个和《切韵》入声调类有传承关系的调类；这些不同时期、不同方言中的入声调类，都拥有各自的入声调值，但调型一般也都是短而急促的。 尽管入声在根据传统音韵学属于“四声”之一，但“入声和非入声的差别更多来自音质而非音调”（王力）。在切韵至广韵时代，入声都稳定并完整（拥有-p,-t,-k三种辅音韵尾）存在于中原的方言中。但是由于当时的具体调值已经不可考，我们便无法得知入声与其他声调在当时是否拥有相同的调值。在现代汉语方言中，有不少是保留入声的（有的完整保留辅音韵尾以及区别于其它声调的调值；有的失去或正在经历辅音韵尾丢失但具有区别于其它声调的调值等）这可视为入声作为声调存在的必要性。

A checked tone, commonly known by its Chinese calque entering tone (simplified Chinese:入声; traditional Chinese:入聲; pinyin:rùshēng; literally: "the tone of character 入"), is one of four syllable types in the phonology in Middle Chinese. Although usually translated as "tone", a checked tone is not a tone in the phonetic sense but rather a syllable that ends in a stop consonant or a glottal stop. Note that separating the checked tone allows -p, -t, and -k to be treated as allophones of -m, -n, and -ng, respectively, because they are in a complementary distribution in which stops appear only in the checked tone while nasals appear only in other tones. Because of the origin of tone in Chinese, the number of tones found in such syllables is smaller than the number of tones in other syllables, and in Chinese phonetics, they have traditionally been counted separately.