A point $P$ on the algebraic set $V(f_1, \dots, f_m)$ of expected dimension $d$ is nonsingular if the Jacobian matrix at $P$ has rank $n - d$.
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A singular point on $V(f_1, \dots, f_m)$ is one where the Jacobian fails to achieve the expected rank $n - d$.
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A variety is smooth (of dimension $d$) if every point of $V(f_1, \dots, f_m)$ is nonsingular, i.e. the Jacobian has rank $n - d$ everywhere.
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Intrinsic nonsingularity: a point $P \in V$ is nonsingular relative to chosen generators $f_i$ of the ideal of $V$ when the Jacobian has rank $n - d$.
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Intrinsic singularity: a point $P \in V$ is singular when the Jacobian of a chosen generating set of $I(V)$ has rank different from $n - d$.
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An intrinsic notion of smoothness: every point of $V$ is nonsingular with respect to a chosen generating set of the ideal $I(V)$.