improvement的含意主要有以下两种
1 [ uncountable ] the act of making sth better; the process of sth becoming better
2 [ countable ] a change in sth that makes it better; sth that is better than it was before
Oxford Advanced Learner’s Dictionary, 8th edition
而progress的含义是
1 the process of improving or developing, or of getting nearer to achieving or completing sth
2 movement forwards or towards a place
从以上可知improvement的基本意思是从不完善到更完善的过程或变化，而progress是指与要实现的目标或要达到的目的地比以前更接近了
以上单词英语定义引自英语牛津词典