Scale In: means buy more shares as the stock progresses in your direction. Its better to buy 50% position initially and then buy 33% and 17% as the trade favors us. One may also buy in three equal parts of 33% each.
Scale Out: means exiting from a profitable position in pieces. Its better to sell 17%, 33% and then 50% to take the full profit potential of a trade. Some traders prefer to sell in three equal parts of 33% each which is perfectly fine.
Average In: means adding more shares into a losing position.
All In - All Out: means buy all shares in a single trade and then sell all of them in one trade while taking profit.
Its a good practice to trail stop loss as the first part of profit is booked.
Generally its not preferred to average in a losing position but its still a very common practice among retail traders.
I hope this information will be useful for some traders/investors.
Regards