The term "deceiving" is a very broad one, covering potentially any technique used to provoke the opponent out of an advantageous or well defended position. Meyer discusses deceptions at length in his Rappier section of the 1570 Text, linking it with elements from the preceding Longsword and Dussack sections and expanding on the broader concept of deceptions provided early in the text.
The principle behind deceptions is that an opponent who is prepared in his stance has essentially fortified his position against us. As such he has certain advantages because it is when we attack that we tend to be most at risk. An attack forces us to abandon our own fortification, leaving openings to be exploited. Italian fencing styles from around the same period recognised this and described attacking as disarraying the body. In these styles defensive play was much lauded.
The German tradition, however, adopts a more proactive philosophy. If an opponent is fortified against us then we can engage in combative sleight of hand, forcing him to defend one set of openings, while we actually exploit others. This taking of the initiative (Vor) is a fundamental concept; by forcing his reaction in a certain way we dramatically prune the available list of techniques he can effectively use, reducing our own cognitive load and improving our reaction times.
In his section on the four types of opponent Meyer specifically says that deceptions are useful against those who refuse to make any attacks, as well as people who chase the sword with parries. Against shrewd opponents they are less useful.
The text tells us that there are two broad categories of deception.
Deceiving with the Sword
The first type of deception is performed with the weapon itself by making false attacks which draw the opponent's defence, thus allowing us to attack a vulnerable opening.
These methods display varying levels of sophistication ranging from simply starting a cut at one opening, then quickly moving off to cut another opening, through to engaging in the bind and tricking them into thinking you are leaving it, only to redouble the original attack after achieving superior blade position.
In Meyer's terminology if we make a cut intended to draw a defence it is known as a Provoker, however in common fencing usage we might also use the term feint.
As a general rule when we deceive with cuts we are advised that when we make a provoking cut we should follow with an attack to the opening the opponent just left. So, for example, if my opponent stands in a guard with his sword at his right shoulder, and I attack with a Zornhauw from my right to draw his defence, then I should attack his upper right opening, as this is the point from which he departed (so his momentum is moving directly away from it). In Meyer's words:
"He is most open in the part from which he sends in his stroke. This is a very noteworthy precept, which you shall study diligently and to which you shall give attention..."
Within the deceptions with the sword listed in the longsword section we find:
Deceiving with the Body
The second type of deception involves using our posture and body language to deceive our opponent. This can be both a passive and an active deception.
As a passive action, for example, we might hold our blade too far to one side or the other, subtly inviting an attack. We know that different stances leave different openings so I might, for example, hold my sword out in a point-offline pflug position, thus exposing myself to a thrust. This is a very subtle way of taking the Vor compared to typical interpretations of earlier German work and shows considerable Italian influence.
As an active deception we can misdirect with body language by seeming like we're going to do a thing, then not doing it at all. We might, for example, look to their high openings, then cut to the lead leg without changing our gaze. LIkewise we may seem to be ready for a long step, but instead step short and thus evade their defences.
Often this kind of deception benefits from establishment of a rhythm. We might show that we perform a high cut in a particular way time after time only to be parried, then as we seem ready to perform another we instead perform a low cut.
We see this repetitive action throughout the sword texts of Meyer, with patterns of slashing up, or parrying, or moving back and forth being established then broken to our advantage.