Bitcoin gambling refers to any bitcoin activity which involves an explicit risk of loss, governed by purportedly random events, to the capital brought into the gambling activity by the gambler.  

Don't ever gamble.  If you work hard to earn your bitcoin, then don't risk if for a gambling activity.

Many of the gambling activities have withdrawal limits set in such a way that you cannot withdraw the fund until you have participated in enough rounds of the gambling that the probability of having lost the capital before you could make a theoretical withdrawal is very near to 100%.  This means that from the time you start the game, you've already thrown away your capital, and any labor.  

Speculation is any bitcoin activity which involves and explicit risk of loss, governed by events which are not random, but are which are not totally predictable.  Speculation may involve so called "derivatives", which ownership rights as to one or more contingent revenue streams.   Because derivatives require that you trust intermediaries who usually have not identified themselves, and who have given little information as to how they assure the safety of your funds, you should not engage in this type of speculation.

There is one other type of speculation.  That is if you have bitcoin in an exchange, and you trade that bitcoin, with a low conversion fee, for other cryptocurrency.  You could lose all of your capital if the currency goes belly up, with many surely will... but your hope is that the value of the other cryptocurrency will go up faster than that of bitcoin.  This is risky... and you mostly shouldn't do it... but if you have some insight into a limited number of cryptocurrencies, and you genuinely believe that they will appreciate... this is ok to do on a limited basis.  

A limited basis means that you put only a small portion of your assets at risk, and you select investments that have a plausible chance at appreciation, as determined by your market research.