Unanimity is principle from Voting Theory that is the same as Dominance:
If a candidate $a$ is always preferred by the majority to $b$, then we can say that $b$ is dominated by $a$ and never consider $b$ again
ParetoOptimal Solutions
In MultiObjective Optimization and MultiCriteria Decision Aid there could be many "best" solutions  these solutions are called the ParetoOptimal solutions
Consider this example:

 the two alternatives along the blue line form the paretooptimal set

 the solutions in blue circles also form the paretooptimal set
Dominance
 for the second examples we can say that $b$ dominates $c$:
 $b$ has the same level of quality, but it is cheaper
 we can remove all dominated solutions from the solution space and this will give us the Paretooptimal set of solutions
 in MOO this is also called the set of efficient solutions
 dominance
 $a$ dominates $b$ $\iff \forall i: f_i(a) \geqslant f_i(b)$ and $\exists i: f_j(a) > f_j(b)$
 i.e. for all criteria $a$ is at least as good as $b$, but there's at least one criteria at which $a$ is strictly better than $b$
This is not always good. Consider this example
 you're looking for an apartment to rent
 you consider price and distance to work (want to minimize both)

 in this case $c$ is dominated by $a$ and $b$:
 $b$ is very cheap, $a$ is very close
 $c$ is a good compromise, but it's dominated
Another example
 suppose we're choosing a car
 there are 4 criteria: price, power, consumption, comfort
 there are 6 alternatives

Price 
Power 
Consumption 
Comfort

Avg A. 
18 
75 
8 
3

Sport 
18.5 
110 
9 
2

Avg B. 
17.5 
85 
7 
3

Lux 1 
24 
90 
8.5 
5

Exonomic 
12.5 
50 
7.5 
1

Lux 2 
22.5 
85 
9 
4

We see that Avg B is always better than Avg. A
 then nobody will ever choose Avg A: A is dominated by B
No other alternative can be eliminated this way
This principle is as well applied in the Game Theory
Notation:
 $A_i$  set of strategies for player $i$
 $u_i$  the utility function of $i$
 $a, b \in A_i$  two strategies in $A_i$
 denote $A_{i}$ as the set of all strategies for other players
 Strict dominance
 $a$ strictly dominates $b$ if $\forall c \in A_{1}: u_i(a, c) > u_i(b, c)$
 in other words: $a$ strictly dominates $b$ is for every action that other players can take, the action $a$ gives $i$ better payoff than $b$
 Weak dominance
 $a$ (weakly) dominates $b$ if $\forall c \in A_{1}: u_i(a, c) \geqslant u_i(b, c)$
If $a$ dominates all other strategies $b$ of the player $i$ then it's dominant
Pareto Optimality
In Game Theory there's also a notion of Pareto Optimality
Suppose you see a game as an outside observer, not a player
 Can we say that one outcome $O$ is better than some other outcome $O'$?
ParetoDominance
 suppose there's one outcome $O$ that is as good as some other outcome $O'$ for all players
 but there's one agent $i$ who strictly prefers $O$ to $O'$
 then $O$ is considered better than $O'$
 and $O$ paretodominates $O'$
ParetoOptimality
 outcome $O^*$ is paretooptimal if there is no other outcome that paretodominates it
 a game can have more than one paretooptimal outcome
 for ZeroSum Games every outcome is paretooptimal
Problems
Close Contenders
$b$ is a close contender if
 it's dominated by some alternative $a$
 but $b$ is still a good choice
Consider this example:
 $A = \{a, b, c, d\}$
 $A^* = \{a, c, d\}$  efficient (paretooptimal) set of solutions
$c$ 
$e_1$ 
$e_2$ 
$e_3$ 
$...$ 
$e_{100}$

$a$

100 
100 
100 
... 
100

$b$

99 
99 
99 
... 
99

$c$

101 
0 
0 
... 
0

$d$

0 
101 
0 
... 
0

But we see that $c$ and $d$ aren't that good, but both are in $A^*$
 i.e. we should have taken $b$ instead them
Sources