1. system
指令系統がうまく機能していない。The command system is not functioning well.
2. lineage; ancestry; family line
父方の系統を調べてみた。I looked into my father's family line.
3. group (e.g. of colors) (colours); family (e.g. of languages); party; school (of thought)
灰色、白、水色系統の色をしてることが多い。They are often gray, white, or light blue in color.
4. close (evolutionary) relationship
5. a population sharing a common ancestor (in genetics); strain (e.g. bacterial)
寒さに強い系統の米を育てている。We're growing a cold-resistant strain of rice.