A tech card is a card added to a deck specifically in order to counter the current meta. Tech cards may be simply alternate inclusions in the deck, or sub-par substitutions the use of which is borne out by their effectiveness in the meta.
Tech cards are often included in small amounts to modify an existing deck to counter currents trends in the meta. For example, when there is a strong trend toward decks revolving around large numbers of minions, is often added to decks to counter this type of play. However, Mind Control Tech is not usually included in decks unless the meta demands it.
is another common tech card, serving as a strong counter to decks focusing around burst damage from spell combos, as seen in certain rogue combo decks, as well as working against any spell-oriented deck to some degree. Unlike Mind Control Tech, Loatheb is often included in decks as part of their standard build, or automatically included as a type of tech card which functions well enough against multiple archetypes to earn a regular place in decks.
Many deck guides present a core deck, including all the key cards for that deck to function, and then a number of tech cards or options. Depending on the meta, players may swap some of the regular cards out to make room for some tech cards. More experienced players can make decisions regarding tech cards on the fly, coming up with their own solutions to counter the current meta.
Tech cards represent a tweaking of decks to counter the meta. When the main theme or function of a deck is changed to counter current trends, this tends to instead lead to the creation of a new type or sub-type. Many players will also simply switch to a different deck type or class entirely in response to changes within the meta. Tech cards can allow players to stay within their preferred deck type, by reducing the deck's vulnerability to another popular type.
The use of tech cards in itself forms part of the meta. For example, combo-oriented rogues may learn to expect interruptions from Loatheb, and adjust their decks to better work around it. Tech cards also affect the meta against decks they were not intended to counter, themselves becoming a predictable part of the current trend. In some cases a second tier of tech cards may start to be included, in order to counter the tech cards that were included to counter the original change in the meta.