Děngchā shùliè zhōng, měi yí xiàng yǔ qián yí xiàng de chā dōu xiāngděng.
In an arithmetic sequence, every term differs from the one before it by the same amount.
Tips
usage
Almost always seen in 等差数列 "arithmetic sequence". Its partner is 等比数列 "geometric sequence", where the ratio stays the same. The fixed difference itself is the 公差.