topic marker
The particle は marks the topic of a sentence, telling what the sentence is about.
は is the topic marker. It introduces what you are talking about, and the rest of the sentence gives information about that topic. For example, in 私は学生です (watashi wa gakusei desu), 私は sets the topic as 'I', and the sentence says 'am a student'. The topic can be a subject, object, or even a time or place. When the topic is also the subject, it replaces the subject particle が. When it is an object, it replaces を. So you often see は used where the role is clear from context.