As a motivation, here is an example:
- Click Here To Show Diagram Code
[go]$$B
$$ +---------------------------------------+
$$ | S X S S S X X X M O . . . . . . . . . |
$$ | X X X X X X S X M . . . . . . . . . . |
$$ | S X M M M M M M M O . . . . . . . . . |
$$ | M X M M M M M M M , . . . . . , . . . |
$$ | M M M M M M M M O . . . . . . . . . . |
$$ | . O O . O . O . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ +---------------------------------------+[/go]
If considered generously, the 'potential eyespace' of the black group consists of all marked intersections. The squares denote the group's four 'lakes', where each connected part of squared intersections is a lake.
- The upper left lake is one eye.
- The upper lake is worth 1.5 eyes.
- The left lake is worth 0.5 eyes.
- The lower right lake is worth 0.5 eyes.
The lakes are parts of the eyespace that, in a life and death situation, tend to be the parts with good potential for becoming eyes. If there is only one lake, the defender wants to partition it, while the attacker wants to convert it to (create) a nakade:
- Click Here To Show Diagram Code
[go]$$B
$$ +---------------------------------------+
$$ | S S S X . . . . . . . . . . . . . . . |
$$ | X X X X . O . . . . . . . . . . . . . |
$$ | . . . . O . . . . . . . . . . . . . . |
$$ | O . O , . . . . . , . . . . . , . . . |
$$ | . O . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |[/go]
Black wants to partition the lake, White wants to create a nakade. The outside can be called 'potential eyespace', but usually Black cannot construct additional lakes there.
"A LAKE is a connected part of the potential eyespace of the defender's group that is, or can easily become, visually surrounded by his stones [...]"
John has mentioned 'futokoro', but I have never heard of this term; maybe it has always been translated to 'eyespace', 'eye' or something similar. Would you now say that it has about the same meaning as 'lake'?
An eyespace can, but need not, contain lakes.
Presumably, I use nakade with a somewhat different meaning from the one you use. This, however, does not make my use wrong. I have seen different uses in the English literature. Therefore, when I use nakade, I also explain the meaning that I use:
"Simply speaking, a NAKADE is a lake, so that
1. the defender can fill all but one of its intersections,
2. the defender cannot partition it and
3. there cannot be a seki or ko in it."
Unlike you have guessed, I do not use nakade as a shape term. As you can infer from the approximative definition, I define it as a lake, i.e., as a part of the board, or you might say: "a set of intersections" or "connected part of the potential eyespace".
Furthermore, I use the term "create a nakade" for a play that, surprise, does create a nakade. I.e., I would describe the part of the board just before the move as "a part of the board that a play of the kind 'creating a nakade' can transform into a nakade". The previous example is such a part of the board.
The clarity of restricting the meaning of 'nakade' to a part after the interesting play allows us to perceive well the kind of play 'creating a nakade'. This is what the attacker wants: to make a play that creates a nakade. With this clear understanding of a move meaning, solving life and death situations is eased.
Other uses of 'nakade' exist, but I have found none else similarly useful when thinking about how to solve an LD problem.
Whichever use of nakade somebody (or a particular text) uses, it is bound to be in conflict with other uses of the word. This is a bit unfortunate, but it cannot be avoided, because we are in the age of transition from ambiguous terms to terms with clear meanings. During the transition phase, different people might prefer different uses. Well, this is not ideal, but it is much better when everybody, who uses a term regularly, declares the meaning of his use than continue ambiguous use of undefined terms in a text.
The meanings of 'eye', 'nakade' etc. are not well established in the go world yet. Also 'eye' has a (great) variety of meanings from "potential eye" (during the middle game) to "final eye" (as in scoring positions after completely finished yose). A potential eye can, but need not, become a final eye. Similarly, there are potential versus final eyespace of a group. Other varieties of meanings exist.
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as 0.5 eye (at least). 
in the top left is called a 7 point nakade. 
in the bottom left is called a 6 point nakade. Both of these are examples of the root meaning. The position in the bottom right is called a 5 point nakade. The position in the top right is called a 4 point nakade. These are accrued meanings, OC. 
) is a big wet place where I could drown if I’m not careful. A few islands would be helpful … guess I must read up RJ’s definition.
I wouldn’t have expected this.