What is the difference in meaning between 練習, 訓練 and 実践?
練習｛れんしゅう｝： 学問｛がくもん｝、技芸｛ぎげい｝、運動｛うんどう｝、スポーツなどを、くり返｛かえ｝して習｛なら｝うこと。 A kind of practice to repeat study, an art, physical exercises, athletics or sports, and learn it
訓練｛くんれん｝： 習熟｛しゅうじゅく｝させるため、実際｛じっさい｝にその事｛こと｝をさせて鍛｛きた｝えること。 A kind of training where a trainer lets you really do something and lets you brush the skill of it up, in order to master it
実践｛じっせん｝： 実際｛じっさい｝の情況｛じょうきょう｝のもとでそれを行｛おこな｝うこと。 A kind of real activity to perform something under the real situation
実践 is clearly different from the other two. 実践 is practice as opposed to theory. It's practice as in "bring it into practice", "daily clinical practice", etc. It refers to actually doing something instead of thinking or simulating. 実践的 means practical as opposed to theoretical.
練習 and 訓練 are similar and often interchangeable. But 練習 is closer to practice and 訓練 is closer to training. 練習 is actually doing some physical activity again and again to be able to perform it better. 訓練 tends to sound more organizational and/or occupational, and it sometimes includes learning something in a classroom. 訓練 does not necessarily imply you do one thing many times. If you've just bought your first guitar as a hobbyist, what you will do is usually called 練習. What an astronaut will do before going to the space is usually called 訓練. 訓練 often has a clear goal (an expert doesn't have to do 訓練), but 練習 is something you may have to do throughout your career.