eat out = 不在家里吃，是在餐厅里吃
eat outside = 在室外吃，不在室内吃
比如去（公园）吃个picnic，你可以说：Let's eat outside. 我们在外面（室外）吃吧。
或者在阳台上，也可以说：Let's eat outside.
想去餐厅吃的话，你可以说：Let's eat out tonight. 我们今天下馆子吧。
e.g. I can't be bothered to cook tonight, let's eat out.
我懒得做饭，我们出去吃饭吧。
Both is fine.
Both are fine. / Either is fine. / Either are fine. √
