If you're a fan of baseball prospects, like I've been known to be, abbreviations are common-place. You don't want to be known as an AAAA player or be listed as a 4C or 1B/OF/DH type. TINSTAAPP and YCSS are abbreviations you really don't want to hear either.
When mentioning a pitching prospect, you'll hear "TINSTAAPP" when someone starts talking about their projected spot or numbers. TINSTAAPP stands for "There is no such thing as a pitching prospect," meaning that noone should discount or really read into a pitchers' minor league stats because it doesn't really matter until the pitcher actually makes it to the majors. The criteria for a promotion for a pitcher differs from pitcher-to-pitcher and level-by-level. Stats like ERA and W-L record may be ignored, when a promotion is determined by K/BB ratio or K% on change-ups. Development is key, stats can often be superficial.
Why does TINSTAAPP exist? Well, there's been thousands of pitchers who have never pitched in a major league game but have had stellar careers in the minors. There's been just as many that have had stellar(albeit rushed) minor league careers to flame out and get absolutely crushed in the majors. Where do you think relievers and closers come from? College?
Pitchers are a strange breed, you never known when things "click" for them. A blue-chip HS pitcher could be a strikeout machine, throwing no-hitters and double-digit strikeout games against HS competition to being completely out of baseball in 3-4 years because his "click" happened too early and professional baseball's immenseness completely scared them. How about the college pitcher that has the right size and pitches, but the stats aren't happening. He could be 3 years into his minor league career and the click happens. He learns, from an arm injury, that his change-up is a strikeout pitch and not his fastball or curve. All this said, Knuckleballers comeout of nowhere and can pitch for decades.
YCSS is "Young Catchers Stagnation Syndrome" and sometimes is combined with Tall Catchers. More often than not, YCSS has created a great number of our power-hitting first basemen or other positional players.
YCSS occurs when a team with an All-Star level catcher has an up-and-coming blue-chip catching prospect being blocked or having their development slowed down by the incumbent. YCSS sufferers either get moved to another position(best-case scenario) or start regressing from repeating levels and start losing their blue-chip status(worst-case scenario).
A legit blue-chip catching prospect is a dying breed, seeing as most catching prospects are "all-bat-no-glove" or vice-versa. To be good at both starts your legs/knees' time-clock, due to the stress squatting for an entire game and the running of the bases, and you only have a matter of time before you're forced to move to another position or retire. So rushing them through the minor league system is common-place is expected. Why waste their time and legs in the minors?
Tall catchers have an even shorter time-clock and YCSS happens to them over 50% of the time.
Abbreviations in baseball sure can be fun, huh? I have yet to even start talking stats.