congress
名词
1.(正式)会议;代表大会[C]
a medical congress on AIDS 讨论爱滋病的医学会议
2.(大写)美国国会[E]
a Member of Congress 美国国会议员
conference
名词
1. (正式)会议;讨论会,协商会[C][(+on)]
I attended a conference on disarmament last week. 我上周参加了一个裁军会议。
2. 讨论,会谈[S1][(+with)]
The teacher was in conference with parents after school. 放学后教师和家长进行了商谈。
3. (学校,教会,体育队等的)联盟[C]
而session指的则表示具体某次会议或者讨论,更为狭义些。比如第十一届全国人民代表大会第一次会议:The first session of the 11th National People's Congress. 又比如一次大会conference有好几轮会议或讨论,单次的会议都是用session或者meeting来说的。