轻声，, it's normally pronounced short and light in special conditions, it's usually unmarked.

e.g: 爷爷、奶奶、爸爸、妈妈、哥哥、姐姐、弟弟、妹妹 这些词语中，第二个字都是“轻声”，要读得轻些、短些。

for example, in english, when I ask u how to pronounce "don't" u will say : dont but if I ask u how to pronounce "I don't know" u will omit "t" of "dont" in chinese, such as 好么 好的 好了 etc these 么 的 了 are neutral tones