A group, lineage, or system; often used as a suffix in compounds to indicate a category or lineage (e.g., -type, -lineage).
彼はロシア系の血筋だ。
He is of Russian descent.
このブランドはストリート系の服が多い。
This brand has many street-style clothes.
家系図を調べて自分の系を確認した。
I checked my family tree to confirm my lineage.
In mathematics, a corollary: a result that follows directly from a theorem or proposition (specialized use).
この定理の系として次の命題が導かれる。
The following proposition can be derived as a corollary of this theorem.
In geology, a 'system' referring to a range of strata corresponding to a particular geological time period (specialized usage).
この地層は白亜系に属すると考えられている。
These strata are thought to belong to the Cretaceous system.
In taxonomy, a term sometimes used for a series grouping related organisms (a taxonomical series).
この植物は同じ系に分類されている種が多い。
Many species of this plant are classified within the same series.