Answer:
"his pond fish’d by his next neighbour" refers to a man's neighbor committing adultery with the man's wife.
The language technique employed here is a figurative expression or a figure of speech called metaphor.
Step-by-step explanation:
The above line is found in "The Winter's Tale" by Shakespeare.
Metaphor is the usage of words to describe somebody or something which are not alike or related. For example, one can say that "kisses are the flowers of affection." In this instance, "kisses" are described as "flowers". But, they are not related in any way. It is only a metaphorical meaning that one can derive from the expression upon reading it. Flowers are fruits or products from trees. Kisses are products from affection, unless it is Judas' kiss.
One important point to differentiate a metaphor from a simile is the non-use of these two words: "like" and "as." Similes must make use of them. An example with the above metaphor is to say, "kisses are like the flowers of affection."