有损数据压缩方法是经过压缩、解压的数据与原始数据不同但是非常接近的数据压缩方法。有损数据压缩又称破坏性资料压缩，也有简称有损压缩。即将次要的信息数据舍弃，牺牲一些质量来减少数据量，使压缩比提高。这种方法经常用于因特网尤其是流媒体以及电话领域。在这篇文章中经常成为编解码。它是与无损数据压缩对应的压缩方法。根据各种格式设计的不同，有损数据压缩都会有代间损失——压缩与解压文档都会带来渐进的质量下降。

In information technology, lossy compression or irreversible compression is the class of data encoding methods that uses inexact approximations and partial data discarding to represent the content. These techniques are used to reduce data size for storage, handling, and transmitting content. Different versions of the photo of the cat at the right show how higher degrees of approximation create coarser images as more details are removed. This is opposed to lossless data compression (reversible data compression) which does not degrade the data. The amount of data reduction possible using lossy compression is often much higher than through lossless techniques.