Context : Windows 10 was available in 190 countries and 111 languages upon its launch, and as part of efforts to ``re-engage'' with users in China, Microsoft also announced that it would partner with Qihoo and Tencent to help promote and distribute Windows 10 in China, and that Chinese PC maker Lenovo would provide assistance at its service centers and retail outlets for helping users upgrade to Windows 10. 
Subject : Windows 10 
Relation : series
What is the series called that Windows 10 belongs to?