What does the measure word 一片 mean? and how to use it? In the textbook, we learned that 一片 is the measure word for thin, flat objects such as leaves. But it seems to mean differently in 一片草地. 

What does the measure word 一片 mean? and how to use it?
About 一片, there are some explanations:


Refers to flat and thin (eg: 一片肉)
Refer to the ground surface (eg: 一片空地)
Refer to flaky patches (eg: “黄河远上白云间，一片孤城万仞山。”---王之涣 《凉州词》)
Refer to diffuse scattered (eg: 一片红光)
Refer to gather together (eg: 响声连成一片)
Refer to mood, the mind (eg: 一片心意)
Refer to language (eg: 自做一片文字)
Refer to the whole piece (eg: 军民打成一片)


Hope that can help.