We know one thing is for sure: "far out" isn't beach lingo for something totally rad in Frost's poem. Instead, "Neither Out Far Nor In Deep" gets us thinking about limitations, in particular when it comes to human perception and understanding.
After all, we're not X-Men with superpowers that allow us to see through, well, everything—to the truth. As far as sight goes, we can only see the surface of things, and at a relatively close distance to boot. The same goes for truth-seeking, as it turns out. We can only grasp bits and pieces of life's mysteries and truths. Just the tip of the truth iceberg, as it were.
And of course by the last stanza, the speaker drives home the point of the poem's title by plainly stating, "they cannot look out far" and "they cannot look in deep." So by the end we're able to see the folly of mankind a bit more clearly as they stare at the sea, and are only able to see the ship that bobs along the surface. Silly people along the sand…