理科 = science
離れ = distancing from sth, independence of sth, disinterest in sth
理科離れ literally means keeping distance from science. This refers to a national issue where young people have a tendency not to choose study or career paths that are related to science.
Hmm... I don't know exactly when this problem arised nor to what degree. For more information you can read the ja.wikipedia.org entry of 理科離れ. It's in Japanese though.