Warning: This one is a pretty dry read, but it clears up what I see as a fundamental misunderstanding among trainees.
Anyone that follows my writing knows that I am big on the correct usage of specific language. Many claim that what I argue are simple semantics, when the reality is that incorrect language breeds misunderstanding, which results in stagnation and eventually decline in a trainee. It is due to this that I feel it is necessary for me to establish the difference between cardio and conditioning as I understand them, in terms of both what they are and how they are used.
"Cardio", when used as a verb, refers to the act of intentionally elevating one's heart rate through exercise for the purpose of improving their cardiovascular system. It functions in language in a manner similar to "strength training". There are various methods employed to accomplish this goal, to include jogging, walking, swimming, cycling, boxing, etc. What movement one uses to get there isn't the concern, simply that one is able to get their heart pumping.
When used as a noun, cardio takes on a far more all encompassing meaning. Whenever someone is physically exhausted from a task, they claim to need to work on their cardio. When someone displays great endurance at a task, their superior cardio is applauded. It is one of the first (and many times ONLY) answers given toward fat loss, and one of those things that HAS to be a part of every program.
It is here that the confusion starts and leads to poor training decision. What many consider "cardio" the noun here is in fact conditioning. Conditioning, as a noun, would mean the ability the engage in a specific activity for longer periods of time, along with be able to recover between training sessions from this activity. For the discussion on lifting, it would mean your ability to recover between sets, in terms of both the time it takes to do so and how fully you are recovered. Extrapolate this to other sports as applicable. Running conditioning would make you able to run longer and recover better from runs, boxing conditioning means lasting for longer rounds, etc.
How could this confusion exist? It's due to the fact that there is a presupposed direct carryover from any type of cardiovascular training to your "endurance". This is because of a false notion that endurance is some sort of general quality an athlete possess, when in reality, it is very much dependent on the activity being performed. The reality is, even if your cardiovascular system is very healthy and capable, it's ability to influence your training is limited to the ability of the rest of the systems involved in your activity. If the local muscular endurance of the muscles involved in your activity is shit, your body will quit well before your heart, but the impact is still the same to the outside observer; you "gassed out".
This is why it becomes vital to employ "conditioning", the verb. Though conditioning may have a similar impact to the cardiovascular system as "cardio", the reason why it does has a substantial benefit. Whereas movement selection was inconsequential when it came to cardio, it is crucial when it comes to conditioning. When one engages in conditioning, they utilize a movement that mimics the overall goal of the trainee or utilizes similar muscle groups.
As an example, for an aspiring powerlifter, sled drags, car pushes, kettlebell swings, prowler work, tire flips, etc, would all be great choices for conditioning. They all heavily utilize the posterior chain, and many movements mimic the explosion or hip hinge found in the squat or deadlift. They develop the local muscular endurance of the necessary muscles and also improve the cardiovascular system, effectively contributing to one's "endurance". One of the other benefits of these specific selections is that they are concentric only, which means that your conditioning work is going to have limited negative impact on your recovery between workouts, as the eccentric is what is primarily responsible for muscle soreness.
With this understanding of the two terms, one understands how there is definitely a possibility for overlap of the two terms. One can engage in cardio that is also conditioning work for a sport, with a runner going on a run being an obvious example. One can also perform conditioning work that has a cardiovascular benefit, with the prowler being a great way to elevate your heart rate. The difference exists in the intent of the trainee. If you are trying to improve your endurance as it applied to lifting and go for a run, you've pretty much failed. This is why the concise usage of proper language becomes imperative to improve performance, and why it's also vital for one to get their mentality correct regarding their training and goals to be able to make the correct decisions on what to implement.